The First evidence of marine Badenian transgression near Koceljeva (Central Paratethys, western Serbia)

1 Natural History Museum, Njegoševa 51, 11 000 Belgrade, Serbia. E-mail: gordana.j@nhmbeo. 2 Geological Survey of Austria, Neulinggasse 38, A-1030 Vienna, Austria. E-mail: stjepan.coric@geologie.ac.at 3 University of Tuzla, Faculty of Mining, Geology and Civil Engineering, Department of Geology, Univerzitetska 2, 75000 Tuzla, Bosnia and Herzegovina. E-mail: sejfudin.vrabac@untz.ba Abstract. This paper presents the irst detailed biostratigraphic investigation of deposits cropping out in stream Sumijevac near Koceljeva (western Serbia). The most important fossil communities and their signi icance are presented. New biostratigraphic results have been achieved by the study of calcareous nannoplankton, foraminifera and mollusks fauna which clearly indicate the presence of the lower Badenian zone (Lagenid Zone), and de ines preciously time of the marine transgression in this area. Further, the revised age of the sedimentary deposits presented here provides the necessary background information for future research of the Badenian sediments of Serbia and neighbouring regions.


Geological setting
During the middle Miocene, the Paratethys looded different types of basement in Serbia and a normal marine regime developed in the area (ANĐELKOVIĆ et al., 1989), as a result of the increase in global sea level (KOVAČ et al., 2007). The locality Sumijevac provides valuable geological and paleontological data of Koceljeva area palaeoenvironments in western Ser-bia during the early-middle Miocene. Similar lower Badenian deposits recently were described in Bosnia . Well-documented Badenian lithostratigraphic units are recognized in several basins such as: Podrinje, Kolubara, Belgrade and Velika Morava (ANĐELKOVIĆ et al., 1989). In the vicinity of Koceljeva (Kolubara basin), fossiliferous beds are exposed in the valley of Sumijevac Stream. Palaeogeographicaly, this site is located at the extreme southern margin of the Pannonian Basin, and belongs to the Koceljeva Graben that occupies the extreme southwestern part of the Kolubara-Tamnava Basin, constricted between the horsts of Vlašić-Blizonj in the south and Jazovnik in the north (after MAROVIĆ et al., 2007). Sedimentary rocks in the outcrop are represented by polimicrite conglomerates and sandstones. Badenian deposits of the wider area of Sumijevac Stream are rich in fossil records (STEVA NOVIĆ, 1959). However, the palaeontological investigations have not taken place in the area regularly over the last decades, because sediments are only exposed on the banks of the stream and can be seen only at a low water level. GAGIĆ (1968) and PETROVIĆ (1985) investigated foraminifers from this locality and attributed these deposits to the late Badenian. They were generally related to the synrift phase of the Pannonian Basin (MAROVIĆ et al., 2007). This locality is situated at the Basic Geological Map 1:100,000, sheet Vladimirci L 34-124 (FILIPOVIĆ et al., 1973). Koceljeva graben was illed with deposits from the lower Miocene to the upper Miocene. We investigated about 2.8 m thick transgressive middle Miocene (Badenian) deposits ( Fig. 1d) which unconformably overlies the lower Miocene freshwater sediments (STEVANOVIĆ 1977).

Material and methods
Middle Miocene (Badenian) deposits of the Koceljeva contain diverse fauna and often have exceptional fossil preservation. Also, fossil material of the Sumijevac Stream is very well preserved and only several specimens show signs of reworking. Research methods have included ield work and laboratory investigation in the Natural History Museum of Belgrade (Serbia), Geological Survey of Austria and University of Tuzla, Faculty of Mining, Geology and Civil Engineering (Bosnia and Herzegovina). Field work and sampling at this locality was conducted during 2017. The procedures adopted for the fossil extraction are in accordance with standard palaeontological sample preparation technique. For the microfossil extraction, three samples were prepared and washed at the laboratory and allowed to dry. Laboratory methods were employed for disintegrating soft sandstone using hydrogen peroxide. After that water is added and allowed to stand for few hours. Samples were washed over a 0.1 mmsieve and picked under the microscope. The specimens were identi ied with age attribution.
Small amounts of sediments were taken for the calcareous nannofossils investigation. Smear slides were prepared following the standard procedure described by PERCH-NIELSEN (1985). The stratigraphical analysis of the nannoplankton zonation is followed by MARTINI (1971), while the foraminifera zonation is based by GRILL (1943).
We recognized ive layers, but lowermost and uppermost parts of the described outcrop have not been investigated. For this research, the authors have chosen only beds rich in fossil remains. All collected material is stored in the collections of Natural History Museum in Belgrade (Serbia). The part of studied specimens of foraminifera are housed in the University of Tuzla, (Bosnia and Herzegovina), while the samples of nannoplankton assemblages are stored in the collection of the Geological Survey of Austria in Vienna.

Biostratigraphy
Biostratigraphic analysis is based on the part of this section with three lithological units recognized and described from the bottom to the top in Figs. 1 and 2. The studied part of the outcrop starts with a ine-grained, weakly cemented polymictic conglomerate (sample 1). Angular and slightly rounded quartz grains which are sometimes transparent and glossy dominate. The grains of quartz, limestone and others rocks are slightly rounded, up to 1 cm in size. Grains of mica are very rarely represented. Besides calcareous nannoplankton and foraminifera the conglomerate contains abundant good preserved shells of juvenile mollusks, fragments of some adult mollusks, disarticulate shells of adult bivalves, echinoid spines, ostracods and otolites. This unit is about 0.5 m thick.
Calcareous nannoplankton is rare, but well preserved and contains Sphenolithus heteromorphus DEFLANDRE, 1953. Nannoplankton  The conglomerate is overlain by a layer of grey, poorly cemented sandstone (sample two) with similar association of nannofossils and foraminifera and much more diverse and better preserved mollusks specimens. Angular and weakly rounded quartz and calcite grains, as well as fragments of mica are detected under the microscope. In common with conglomerate layer, the nannoplankton association is the same. The benthic foraminifera are dominant, whereas planktic forms are represented by the genus Globorotalia. The following species were determined: The third layer at the top of the succession is composed of grey, whitish to yellowish, very inegrained, poorly cemented sandstone. Microscopically, the pronounced dominance of quartz grains, with signi icantly subordinate participation of calcite grains and fragments of mica minerals is observed. These sediments are richer in the calcareous nannoplankton content then previous ones and contain also S. heteromorphus. The list of identi ied species The identi ication of the nannoplankton zone NN5 (MARTINI, 1971), (Fig. 3), was made based on the presence of Sphenolithus heteromorphus and the absence of Helicosphaera ampliaperta in all investigated samples. The last occurrence of H. ampliaperta de ines the NN4/NN5 boundary. Planktic foraminifera are very rare in the Sumijevac deposits, making correlation with the planktic zonation dif icult. Therefore, biostratigraphic zonation is mainly based on the benthic foraminifera which have relatively high diversity in the study section. The associations of foraminifers from the analysed samples also indicate that the sedimentary deposits of Sumijevac belong to the Ammonia viennensis and Nonion commune zone of the early Badenian. The zone is dated as middle Miocene based on the presence of benthic forms, and corresponds to the M5 zone of BERGGREN et al. (1995), on the regional scale (Pa ratethys). Also, the cha racteristic species Lenticulina clypeiformis found only in the lower Badenian of Central Paratethys (CICHA et al., 1998) was discovered in the sample No. 2 (bed 2). In addition, Ammonia with quite large shell is a characteristic form of lower Badenian (PAPP & SCHMID, 1985;VRABAC, 1989

Discussion and Interpretation
In this paper, the Badenian marine sediments from the  (according JOVANOVIĆ et al., 2018). adjacent area of Koceljeva were studied from a biostratigraphy perspective. The lowermost and uppermost parts of the described outcrop have not been investigated due to the lack of fossils. Transition of the lowermost part of the succession towards the irst fossiliferous bed was not recorded. The series of coarse conglomerates a few meters thick are located along the Sumijevac stream, not far from described section. It is possible that conglomerates from the layer 1 (Fig. 2 e) corresponds to Middle Miocene (Badenian). The basal conglomerate contains large rounded clasts with size range from less than 3 mm to over 40 cm. The space between them is illed with smaller particles of other sedimentary materials.
Based on foraminifera GAGIĆ (1968) and PETROVIĆ (1985) attributed these deposits to the Upper Badenian Rotalia beccarii Zone (= Ammonia viennensis). In Vienna Basin, Rotalia beccarii Zone (= Ammonia viennensis) corresponds to the Rotalid Zone, also known as Impoverishment Zone (PAPP & SCHMID, 1985). On the southern boundary of the Central Paratethys, in addition to other foraminiferal zones of Badenian, the local Zone Ammonia viennensis and Nonion commune (VRABAC et al., 2006, as well as the upper Zone Ammonia viennensis are separated (VRABAC, 1989). There are two essential differences between these zones. The irst difference is a palaeogeographic-superposition character. The lower Badenian Ammonia viennensis Zone and Nonion commune Zone were deposited during the transgression of Central Paratethys and transgressively overlain the rocks of different composition and age (EREMIJA, 1987;1987a;VRA -BAC, 1999). In Bosnia, these are followed by the lower Badenian Trilobatus trilobus Zone and Orbulina suturalis Zone (VRABAC, 1999). The upper Badenian Am monia viennensis Zone is deposited during the regression of the Central Paratethys (SENEŠ, 1974;SOKLIĆ, 1988;VRABAC et al., 2015), and conformably overlies the upper Badenian Bolivina dilatata maxima Zone. Another very important difference is a palaeontological character. By the end of the Badenian there was a decrease in salinity, which is why the organic world in the uppermost zone of upper Badenian is considerably poorer than in the lower Badenian zone (VRABAC, 1999) HILGEN et al. (2009), NN zone after LOURENS et al. (2004PILLER et al. (2007), HOHENEGGER et al. (2009), PEZELJ et al. (2013, SANT et al. (2017). which chara cterized lower Badenian forms. All of the above mentioned characteristics are recorded at several pro iles in the northern Bosnia. In this area (Tuzla basin, Ugljevik region, etc.), the lowermost part of lower Badenian is also presented by the Ammonia viennensis Zone and Nonion commune Zone corresponding to the nannoplankton Zone NN5, according to VRABAC et al. (2006, 2011) and ĆORIĆ et al. (2007. This zone is synchronous with the Lagenide Zone of Vienna Basin (GRILL, 1943;PEZELJ et al., 2013).
A characteristic feature is the presence of Corbula gibba and Turritella badensis showing a marked frequency in the deposits. Among mollusks especially the juvenile forms of the opportunistic species  ZACHOS et al., (2008). This diverse fossil material is typical for the Langhian of Central Paratethys (HARZHAUSER et al., 2003). Several thermophilous elements (especially Semicassis, Procardium, Kalloconus, etc.) which were recorded in the Central Paratethys during early Badenian, are identi ied. Several samples of Cubi tostrea, Conus, Persistostrombus and corals collected by Nikola Panić are housed in the Native museum in Koceljeva providing additional information on the assemblages of lower Badenian mollusca. Relatively high molluscan diversity observed in some other localities in Serbia (EREMIJA, 1987) and Bosnia (ATANACKOVIĆ, 1969; is a marker of tropical conditions in the Paratethys Sea during middle Miocene times. These results highlight how important is the study of many different sites situated on the southern margin of the Central Paratethys in order to gain a full understanding of warm climate in luence in the distribution of mollusks fauna. The lithofacial and biofacial characteristics of the studied deposits of the Sumijevac pro ile indicate that they were deposited in a very shallow, coastal part of the infralittoral in the sea with normal salinity. The dominance of Reticulofenestra minuta and Coccolithus pelagicus indicates shallow, marine envi-ronment with rich nutrients input. The majority of the mollusks species in this article like many of the species recorded from the prior papers (EREMIJA, 1977;STEVANOVIĆ, 1959;DOLIĆ & KRSTIĆ, 1985) belong to the genera living in subtropical and tropical seas.
Among mollusks especially the juvenile forms of the opportunistic species Corbula gibba were observed. This is a species with high fertility and an enormous number of eggs and can be settled in rather unstable soft sea bottom. Corbula inhabits soft bottom sediments mixed with molluscan shell fragments (HRS-BENKO, 2006). This bivalve with a sedentary mode of life is very frequent in the Middle Miocene sediments of Serbia and other localities of Central Paratethys. The discovery of carbonated woods in the lower part of the succession (bed 2) also indicates an input from the terrestrial environment near coastal environment of the littoral zone. Atrina pectinata (pen shell) lives embedded in the sediment. The fragile shell of this bivalve is easily damaged by physical disturbance. However, unlike Corbula gibba, juvenile Atrina pectinata in sediments are usualy smothered and the recoverability is likely to be low. Atrina pectinata from Sumijevac section with well-preserved prismatic layers composed of columnar crystals indicates the in luence of weak and moderate currents. The most important palaeoecological change is observed in the increase in size and biodiversity of mollusks fauna, especially in sample No. 3. Turritella assemblages are common with large specimens of Turritella badensis. A high percentage of Turritella representation can also be an indication of a coastal marine environment with a rich nutrients input.
The locality Sumijevac Stream provides valuable evidence of the Koceljeva palaeoenvironments du ring the early Middle Miocene. The marine invertebrate fauna of Sumijevac Stream is among the richest recorded from the Badenian sediments of Serbia. The revised age of the sedimentary deposit presented here provides the necessary background information for future research of neighbouring regions.

This paper presents the irst detailed biostratigraphic investigation of the sedimentary succession
The First evidence of marine Badenian transgression near Koceljeva (Central Paratethys, western Serbia) Geol. an. Balk. poluos., 2019, 80 (1), 1-15 in the Sumijevac Stream, near Koceljeva. The results of new material collected in the 2017 are presented and the biostratigraphical implications are interpreted in more details. The deposits at this locality are abundant in fossils. However, previous investigations had yielded different stratigraphic attributions. The sediments are rich in mollusks, calcareous nannofossils, benthic foraminifera, whereas sporadically occurr ostracods, otoliths and remains of echinids. Prior to these investigations the age of the Sumijevac deposits remained poorly constrained.
The study of Sumijevac succession includes biostratigraphic analysis based on calcareous nannoplankton, benthic foraminifera and pteropods. Biostratigraphically, it corresponds to the lower Badenian (Lagenidae Zone). Some species are very useful biostratigraphic markers, such as nanofosil Sphaenolithus heteromorphus and benthic foraminifera (Lenticulina clypeiformis, Ammonia viennnsis and Nonion commune). The identi ication of the nannoplankton zone NN5 (MARTINI, 1971), was made on the basis of the presence of Sphenolithus heterop morphus DEFLANDRE and absence of Helicosphaera ampliaperta BRAMLETTE & WILCOXON. The last occurence of H. ampliaperta de ines the NN4/NN5 boundary. Furthermore, benthic foraminifera (Lenti culina clypeiformis, Ammonia viennnensis and Nonion commune assemblage) correspond to this biostratigraphic level. Also, the presence of holoplankton species Vaginella austriaca indicates the lower Badenian age of these sediments. This pelagic gastropod was not recorded from the deposits of upper Badenian in Central Paratethys (BOŠNJAK et al., 2017). This is the earliest transgressive event documented in the vicinity of Koceljeva.
In addition, some species or mollusks assemblages have been used as indicators of the paleoclimate in coastal environments. The Sumijevac sediments were deposited in a very shallow, coastal part of the infralittoral with normal sea salinity. The dominance of Reticulofenestra minuta and Coccoli thus pelagicus as well as some mollusks and benthic foraminifera indicates a shallow, marine environment with rich nutrients input. The revised age of the sedimentary deposit presented here provides the necessary background information for the future research of neighbouring regions. We conclude that it is necessary to carry out the revision of the upper Badenian, determined only based on the Rotalia bec carii Zone (= Ammonia viennensis) in neighbouring regions in Serbia (Koceljeva, Rakovica stream near Belgrade, SW Banat, Sopot, Mladenovac, Aranđelovac, Kolubara basin, etc.), as well as in Bosnia and Herzegovina (Prnjavor basin, NE Kozara area, etc.), and Croatia (Borovnjak, etc.).