Pannonian ostracods from the southwestern Transylvanian basin

Pannonian (Late Miocene) ostracods were investigated from 7 outcrops, exposing deep-water lacustrine sediments along the western margin of the Transylvanian Basin. Sedimentological patterns in the outcrops indicate deposition in sublittoral to profundal environments where finegrained, suspension fall-out sediments are intercalated with various types of mass transport deposits, most commonly turbidites. The ostracod fauna, consisting of 30 taxa, is dominated by endemic species of the brackish Lake Pannon. The assemblages indicate a mixture of deepwater (sublittoral to profundal) species, such as Paratethyan Candoninae, and shallow-water (littoral) species, belonging to Cyprideis, Loxoconcha, Amnicythere and Hemicytheria. The mixed character of the assemblages is most probably a consequence of the reworking of littoral specimens into deeper environments, a phenomenon also observed in the molluscan fauna from some of the investigated outcrops. Alternatively, some endemic and extinct species of the littoral ge nera might have adapted to the deep-water environment. A significant decrease in the abundance and diversity of ostracods from west to east is interpreted reflecting increasingly distal environments. The ostracod fauna indicates the Hemicytheria hungarica (2 outcrops), Hemicytheria tenuistriata (3 outcrops), and Propontoniella candeo Zones (2 outcrops) of the lower Pannonian Slavonian Substage. comprises the Middle and Upper Miocene (Badenian, Sarmatian and Pannonian Central-Paratethys stages). The Middle Miocene to Quaternary evolution of the TB is related to the Carpathian orogene (ROYDEN, 1988; SCHMID et al., 2008). During this period it evolved as a compressional back-arc basin (DE BROUCKER et al., 1998; CIULAVU, 1999; SANDERS et al., 1999; KRÉZSEK et al., 2010), and its sedimentary history was connected to the subduction along the Carpathian arc. Although a very high rate of subsidence is encountered during this period, no major extensional faults are reported; instead, most structures are related to salt-tectonics (KRÉZSEK & BALLY, 2006). Middle Badenian evaporites are widespread in the subsurface of the entire TB (GHER GARI et al., 1991; KOVÁČ et al., 2007), and salt tectonics was most effective from the Sarmatian to the Pliocene (KRÉZSEK & BALLY, 2006). Following the fully marine conditions of the Badenian and restricted marine environment in the Sarmatian, the uplift of the Carpathians closed the gateways between the Central and Eastern Paratethys at the end of the Middle Miocene and thus isolated the intra-Carpathian region from the rest of the Paratethys (TER BORGH et al., 2013). With the onset of the Late Miocene Pannonian age, the TB became part of the large brackish Lake Pannon (MAGYAR et al., 1999). The Sarmatian−Pannonian boundary in the TB was traced in a large outcrop of marls and turbiditic sandstones in Oarba de Mureş (SZTANÓ et al., 2005), on the basis of dinoflagellate biostratigraphy (SÜTŐ-SZENTAI & SZEGŐ, 2008), magnetostratigraphy and radiometric dating (VASILIEV et al., 2010), and foraminifer and ostracod biostratigraphy (FILIPESCU et al., 2011). The boundary was unanimously marked on the basis of microfossils. Although the magnetostratigraphic interpretation of the measured polarity pattern is contradictory, high-precision radiometric dating of a volcanic ash deposit from the very top of Article history: Manuscript received July 18, 2015 Revised manuscript accepted April 17, 2016 Available online June 01, 2016


INTRODUCTION
Study of ostracods of the Neogene Paratethys has substantially contributed to the stratigraphic, environmental, and palaeogeographic understanding of this huge and complex marine to lacustrine depositional system (DANIELOPOL et al., 2008a).Of the large brackish lakes that repeatedly formed during the history of the Paratethys, the Late Miocene-Early Pliocene Lake Pannon was probably the longest-lived (MÜLLER et al., 1999;HARZ-HAUSER & MANDIC, 2008).As a consequence, this lake was inhabited by an astonishingly diverse lacustrine biota (e.g.PAPP et al., 1985;STEVANOVIĆ et al., 1990).
The dominantly endemic ostracods of Lake Pannon have been studied and described by generations of palaeontologists, starting with REUSS (1850), and leading to the introduction of ca.500 new species.The taxonomy, environmental requirements, and palaeogeographic distribution of these ostracods, however, is far from being well understood, and needs further study (DANI-ELOPOL et al., 2008a).In particular, the Transylvanian Basin (TB), representing the easternmost part of the early Lake Pannon, lacks modern and well-illustrated documentation of the endemic ostracod taxa.The objective of this paper is to present the Late Miocene (Pannonian) ostracod faunas from several outcrops of the southwestern TB, and to explore their palaeoecological, palaeobiogeographic and biostratigraphic context.

NEOGENE EVOLUTION OF THE TRANSYLVANIAN BASIN
The TB is bordered by the Eastern and Southern Carpathians, and the Apuseni Mountains (Fig. 1).The basin fill can be divided into several tectono-stratigraphic megasequences (KRÉZSEK, 2005;KRÉZSEK & BALLY, 2006), the uppermost one of which comprises the Middle and Upper Miocene (Badenian, Sarmatian and Pannonian Central-Paratethys stages).The Middle Miocene to Quaternary evolution of the TB is related to the Carpathian orogene (ROYDEN, 1988;SCHMID et al., 2008).During this period it evolved as a compressional back-arc basin (DE BROUCKER et al., 1998;CIULAVU, 1999;SANDERS et al., 1999;KRÉZSEK et al., 2010), and its sedimentary history was connected to the subduction along the Carpathian arc.Although a very high rate of subsidence is encountered during this period, no major extensional faults are reported; instead, most structures are related to salt-tectonics (KRÉZSEK & BALLY, 2006).Middle Badenian evaporites are widespread in the subsurface of the entire TB (GHER GARI et al., 1991;KOVÁČ et al., 2007), and salt tectonics was most effective from the Sarmatian to the Pliocene (KRÉZSEK & BALLY, 2006).
Following the fully marine conditions of the Badenian and restricted marine environment in the Sarmatian, the uplift of the Carpathians closed the gateways between the Central and Eastern Paratethys at the end of the Middle Miocene and thus isolated the intra-Carpathian region from the rest of the Paratethys (TER BORGH et al., 2013).With the onset of the Late Miocene Pannonian age, the TB became part of the large brackish Lake Pannon (MAGYAR et al., 1999).The Sarmatian−Pannonian boundary in the TB was traced in a large outcrop of marls and turbiditic sandstones in Oarba de Mureş (SZTANÓ et al., 2005), on the basis of dinoflagellate biostratigraphy (SÜTŐ-SZENTAI & SZEGŐ, 2008), magnetostratigraphy and radiometric dating (VASILIEV et al., 2010), and foraminifer and ostracod biostratigraphy (FILIPESCU et al., 2011).The boundary was unanimously marked on the basis of microfossils.Although the magnetostratigraphic interpretation of the measured polarity pattern is contradictory, high-precision radiometric dating of a volcanic ash deposit from the very top of the one-km-thick Sarmatian sequence (vaSiliev et al., 2010) indicates that the Sarmatian-Pannonian boundary is about 11.6 Ma old, in accordance with recent magnetostratigraphic interpretations from the vienna basin (PauliSSeN et al., 2011) and the Pannonian basin proper (Ter BorGH et al., 2013).
after the isolation event, the water level of lake Pannon gradually rose, controlled both by increased precipitation and subsidence all over the Pannonian Basin system (MaGyar et al., 1999;Garcia-caSTellaNoS, 2006;HarzHauSer et al., 2008).Pulses of tectonic uplift with short wave lengths are recorded by coarse-grained fan delta systems along the basin margins (Maţenco et al., 2010).These fan deltas prograding from the carpathians and from the apuseni Mts.toward the basin centre fed the deep-lacustrine turbidite systems interfingering with hemipelagics/profundal marls.Sedimentary facies of the Pannonian deposits thus reflect deposition in a deep lacustrine setting, including lacustrine deep-water fans (KrézSeK & FiliPeScu, 2005;SzTaNó et al., 2005;KrézSeK et al., 2010).Shallowwater deposits are subordinate and were preserved mostly in the eastern part of the basin.the final infill of the basin did not take place until the end of the Miocene, but these deposits are seldom preserved, except where covered by back-arc volcanics (Kré zSeK and FiliPeScu, 2005;Maţenco et al., 2010;KrézSeK et al., 2010).
apart from Pliocene lacustrine sediments in the southeastern corner of the TB (for a modern review see HarzHauSer & MandiĆ, 2008), late Miocene lake Pannon sediments are the youngest deposits in the basin fill succession.their presentday thickness is usually less than 500 m (KrézSeK et al., 2010).Due to Pliocene to Quaternary uplift, more than 500 m of sediments have been eroded particularly in the northernmost part of the TB (De BroucKer et al., 1998;KrézSeK & FiliPeScu, 2005).erosion is still active today in the basin, where the altitude varies between 300 and 600 m above sea level (Maţenco et al., 2010).
De leeuW et al. ( 2013) tried to obtain better age constraints on the Middle to late Miocene central Paratethyan regional stages (Badenian, Sarmatian and Pannonian) through integrated mag netostratigraphic, radio-isotopic and biostratigraphic research in transylvania.at Mediaş, Sighişoara, and târnăveni, the ostracod assemblages indicated a Pannonian age. in the case of viforoasa and Şoimuş, 3 ostracod biozones were identified following the zonation of KrStiĆ (1985): the Propontoniella candeo zone, indicating the uppermost part of the Slavonian Substage, and the Amplocypris abscissa and Hemicytheria croatica zones, indicating the lower part of the Serbian Substage.

MATERIAL AND METHODS
We have selected 7 outcrops from the southwestern part of the TB, where description of the sedimentary facies and interpretation of the depositional environment was followed by sampling for ostracods, preferably from fine-grained sediments where in situ burial of the shells seemed more probable.
altogether 10 micropaleontological samples (250 g air-dried material) were collected.These samples were washed in hydrogen peroxide (10%), sieved using a 150 μm sieve and oven dried.after a preliminary observation under stereomicroscope, the ostracods were examined and photographed using a scanning electron microscope.a jeol jee 4B vacuum evaporator was used for deposition of gold on the surface of specimens.Pictures were taken with SeM (aMray 1830) at an accelerating voltage of 20kv in the SeM laboratory of the Department of Petrology and Geochemistry, eötvös loránd university, Budapest.
all the ostracod valves, both adults and juveniles, whole and broken specimens were counted from each sample.
Today several small outcrops can be found in the hilly outskirts of the village.They expose an alternation of argillaceous marl and yellow, fine-medium-grained sands, building a 7−8 m thick succession (Fig. 2).given the lack of specific sedimentary structures it is difficult to decide if the sand was transported by gravity-driven processes or just currents/waves/storms.Both the marls and the sandstones are friable and the carbonate cementa-tion is poor.The thickness of sand layers increases upwards from 2−3 cm to 10−15 cm.along the bedding planes plant fragments, branches, and poorly preserved leaf imprints occur together with a rich mollusc assemblage equally consisting of deep-water (Con geria banatica r.HörNeS, Paradacna cf.lenzi (r.HörNeS), Undulotecha pancici (BruSiNa)) and shallow-water forms (Me lanopsis vindobonensis FucHS).our sample was collected from a marl bed in the lower part of the outcrop (Fig. 2).
The ostracod association is well preserved and evenly distributed in the argillaceous marl, reflecting autochthonous or al-  Species of Cyprideis, Loxoconcha and related genera typify marginal ostracod assemblages world-wide (BooMer & eiSeN-Hauer, 2002;BooMer et al., 2005).according to KrStiĆ and STaNcHeva (1990), Cyprideis is common in the marginal parts of the Pannonian basin, but missing from the deep basins.Cyprideis is therefore an indicator of shallow waters.it inhabits mostly brackish (mesohaline) environments, showing the great-   est abundance at salinities of 2− 16.5‰ (WaGNer, 1964), but certain species of the genus may adapt to hypersaline environments (MeiScH, 2000).Pannonian assemblages with Cyprideis, Amplocypris, Amnicythere, Hemicytheria and Loxoconcha were probably highly tolerant of fluctuations in salinity: they occupied estuaries, i.e. semi-enclosed coastal water bodies with a salinity gradient from brackish to freshwater, in the southern part of the Pannonian basin (e.g.Kolubara basin in northwestern Serbia;rundiĆ, 2006).Loxocorniculina is known from brackish water ostracod assemblages of the Paratethys and the eastern Mediterranean (PiPíK & BoDerGaT, 2004).according to Korecz (1991), Candona (Caspiolla) praebalcanica inhabited plio-mesohaline environments, with 15−80 m water depth, and Candona (Caspiocypris) transilvanica inhabited shallow but calm environments.
The entire ostracod assemblage shows a mixture of shallowand deep-water species, probably as a result of redeposition of littoral forms into deeper parts of the basin.Candona (Caspiolla) praebalcanica appears in our material with complete carapaces filled with sediment, a phenomenon indicating rapid burial (Hol-MeS, 2001).otoliths and fish teeth also occur in the microfauna (Pl. 3,.

The Gârbova de Jos/Alsóorbó locality
the 20 m high outcrop is located near the village of gârbova de Jos (46°27'25.58"n,24°17'10.57"e)(Fig. 1). the outcropping succession is cut by a large normal fault of several metres offset, there fore a relatively thick sedimentary succession can be studied (Fig. 3). it comprises clast-supported, graded conglomerates, thick pebb ly mudstones, mud-clast conglomerate, pebbly sandstones, and coarse-to medium-grained and medium-to fine-grained grad ed sandstone beds intercalated with mudstones.individual beds are 1−50 cm thick.Poor normal grading and plane-to crosslamination were recognized.clast size occasionally attains 50 cm in diameter.These boulders are covered by horizontally laminated, deformed mudstone layers.Higher up, mudstone with a few centimetre thick graded sandstone intercalations becomes dominant.the top of the fine-grained sandstones rarely contains small vertical burrows.These beds are the products of sandy-silty turbidity currents, gravelly-sandy turbidity currents, and debris flows.the latter indicates the proximity of the basin-margin slo pe.This interpretation is supported by the composition of the gravel, indicating the apuseni Mts. as a source area.according to Kréz SeK et al. ( 2010), a shallow marine ramp supplied coarse clastics to the open shelf; the frequent, large-volume mass wasting events, however, may suggest a steeper slope, such as that of a fan-delta, and to deeper water, probably below the "shelf-edge".
The studied sample was collected from the lower part of the outcrop, from the dark grey suspension fall out mudstone, which also contained thin shells of deep-water bivalves (Paradacna cf.lenzi, Congeria sp.).
The ostracod association is very poorly preserved with thin and translucent valves. in addition to the fragments, only 48 complete valves were observed in our material.The fauna includes Amplocypris sp., Candona (Typhlocypris) sp., Candona (Propon toniella) sp. and Hemicytheria folliculosa (Fig. 8).
except for the small and ornamented valves of H. folliculosa, which are well-preserved, the valves are damaged and broken.in general, ostracods with smooth, thin and elongated carapaces suggest a calm, relatively deep environment (DaNieloPol, 1980;rundiĆ, 2006).Specimens of the littoral Hemicytheria follicu losa were probably transported into this environment.
the outcrop exposes marl beds and medium-to very finegrained, graded, planar to cross-laminated sandstone layers of 5−10 cm thickness; the latter are interpreted as turbidites.the marl layers are dark in colour due to plant remains (organic matter) (Fig. 4).The depositional setting can be best understood by comparing this outcrop with the previous one, where the same marls and sandstones crop out together with various types of conglomerate (KrézSeK, 2005).
Smooth, thin and translucent valves of Candona have the most significant role in the association, but they are unidentifiable   to species level due to their very poor preservation.The small and ornamented valves of the other taxa are well preserved.Loxocon cha occurs in meso-to euhaline, littoral environments (MorK-HoveN, 1963).Numerous Amnicythere species live in the littoral and sublittoral zones of the Black and caspian Seas at brackish salinity, but some species have been observed in freshwater bays and estuaries.Amnicythere multituberculata (liveNTal) lives today in the central and southern caspian Basins at salinities of 11.5−13.5‰. it is missing in the northern caspian Basin, where freshwater input from volga river effectively lowers salinity (ScHor NiKov, 1964).The freshwater lake ohrid, however, also hosts some endemic species of the genus, such as Amnicy there karamani (Klie) (NaMioTKo et al., 2012).
The central part of the outcrop can be divided into two units (Fig. 6).The lower unit consists of thin beds of mudstone intercalating with very thin, fine-or medium-grained sandstone beds.This unit contains a deep-water mollusc association with Para dacna cf.lenzi, P. cf. abichi (r.HörNeS), Lymnocardium sp., Congeria czjzeki M. HörNeS, C. sp., Velutinopsis sp., Undulo theca pancici, Micromelania sp.The upper unit starts with a wide erosional scour and is composed up of thick, often amalgamated, massive beds of medium-to very coarse-grained, granular sandstone.rip-up mud clasts and water-escape structures are common.Shallow and laterally stepping erosional surfaces are also characteristic.
Sand beds in both units are the products of turbidity currents.The lower unit dominated by mudstones was formed as levee to overbank deposits with rare overspilling thin-bedded turbidites.The upper sandstone represents a complex, laterally migrating deep-water channel fill (KrézSeK et al., 2010; tőKéS, 2013) (Fig. 5).as a whole, a major isolated channel-levee system in a deep, profundal environment can be reconstructed in the outcrop.
Two samples were taken for ostracods; one from the lower part and another from the upper part of the fine-grained overbank sediments (lower unit).
Candona is rare in the lower sample and completely missing from the upper one.Hemicytheria and Amplocypris are dominant in the upper marl bed.Amnicythere occurs in both samples, but it is more abundant in the upper one.Hemicytheria, a representative of the littoral environment, indicates resedimentation processes.
The sampled outcrop displays decimetre to metre thick coarse-grained sandstone and pebbly sandstone beds, up to cobble-sized clasts.These are mostly well sorted with horizontal lamination.The sandstones alternate with bluish grey, bioturbated marls.Some marl layers are laminated.Fish remnants (otoliths, teeth) are common in the studied beds.gravity mass flows and suspension settling alternated in the depositional environment.Three samples were collected from different levels of the bluish grey marl layers.
the cunţa assemblages, especially from the middle and upper parts of the section, differ from our other samples in the diversity and dominance of various Paratethyan candoninae species. in general, the majority of Candona species are freshwater, tolerating a slight increase of salinity, but the endemic lake Pannon candoninae adapted to brackish water (MeiScH, 2000;cziczer et al., 2008).Typically trapezoid-shaped species of the subgenus Lineocypris occur predominantly in the deep parts of large lakes (MorKHoveN, 1963).
The appearance of Cypria in both the lower and upper samples is also a unique feature of the cunţa outcrop.Most species of Cypria live in freshwater (lakes, pools) preferring environments with abundant vegetation, although they tolerate mesohaline conditions as well (MeiScH, 2000).The appearance of this genus therefore may indicate freshwater influence, probably proxi mity of a deltaic environment, in accord with the presence of Unio in the cunţa mollusc fauna (Lőrenthey, 1893).

The Oarba de Mureş/Marosorbó locality
the investigated outcrop is on the right bank of the river Mureş near oarba de Mureş village (46°27'25.58"n,24°17'10.57"e)(Figs. 1, 7).The upper Sarmatian to lower Pannonian outcrops at oarba de Mureş received much attention recently (SzTaNó et al., 2005;Sütő-Szentai & Szegő, 2008;vaSiliev et al., 2010;FiliPeScu et al., 2011).The outcrop sampled (and designated as outcrop "e") is located in the horizontal continuation of outcrop D of SzTaNó et al. (2005), exposing massive and bioturbated clay marl with up to 0.5−1 m thick beds, and with intercalations of a few cm thick calcareous marls (Fig. 7). in this part of the succession sediments indicate deep basin-floor environment without mass-flow events.in one of the calcareous marl layers, molluscs ("Lymnocardium" undatum (reuSS), Congeria cf.banatica) were preserved as moulds.The sample was collected from a massive clay marl bed from the lower part of the outcrop.
The most common species in the assemblage belong to Am plocypris and Candona.Their valves are thin, translucid and often broken.The oblong and elongated carapace shape may indicate benthic dwellers (De DecKKer, 2002).
Ilyocypris cf.expansa seems to be an exotic element in the assemblage, because Ilyocypris is known to live in freshwater, tolerating slowly running water (MeiScH, 2000).valves of the modern species Ilyocypris lacustris KauFMaNN, 1900 were recorded from freshwater lakes at depths of 35−139 m, but the presence of living specimens in deep water environment is uncertain (MeiScH, 2000).its presence in this deep-water assemblage is probably due to reworking from a shallow, freshwater-influenced environment.

Palaeoenvironment and palaeogeography
The overall palaeoecological interpretation of the investigated ostracod faunas is difficult; probably much more samples would be required to understand the ecological significance of these endemic species. in general, the assemblages indicate a mixture of deep-water and shallow-water species.Thin-shelled, smooth Paratethyan candoninae occupied the sublittoral to profundal zones of lake Pannon, from the wave base down to the foot of the slope.The littoral zone was inhabited by forms with thicker and ornamented shells, such as, for instance, Cyprideis, Loxoconcha, Am nicythere, and Hemicytheria.in our samples, the deep-water and littoral taxa occur in various ratio.
interestingly, the mollusc fauna shows similar characteristics across some of the investigated outcrops (lopadea veche, gârbo viţa, and, according to the literature, cunţa).thin-shelled bival ves, known to be confined to deep water environments elsewhere (e.g.Paradacna abichi, Congeria banatica, Undulotheca pancici), occur together (or in very close proximity to) typical littoral, herbivorous snails, such as Melanopsis.Sedimentological patterns in all the outcrops indicate various kinds of mass transport deposits, most commonly interpreted as turbidites.although the ostracod samples were taken from fine-grained, suspension fall-out sediments, reworking and re-deposition of littoral ostracod valves into the deep-water environment is the most plausible explanation for the mixed character of the ostracod (and mollusc) faunas. in this case, the actual ostracod assemblages from the investigated part of the TB highly depend on local taphonomic factors.alternatively, some species of the otherwise littoral ostracod genera may have adapted to living at greater depths; such examples are recorded from the caspian Sea (BooMer et al. 2005).
in terms of the abundance and diversity of ostracods, these outcrops can be divided into two distinct groups: Lopadea, gârboviţa, and cunţa (all the three samples) yielded more than 100 specimens (154 to 665) and at least 10 species (10 to 14), whereas gârbova de Jos, Mihalţ, tau (both samples), and oarba de Mureş yielded consistently fewer specimens (48−100) and species (4−6) from the same amount of sediment (Fig. 8). in addition, reworked littoral molluscs occur in the first group, but they were not observed in the second.the first group of outcrops lie closer to the basin margin, directly on the foothills of the apuseni Mts, where as the second group is located in a more basinward position (although the distance between gârboviţa and gârbova de jos is only a few kilometres).We hypothesize that these differences in abundance and diversity of the ostracods reflect environmental differences, such as deeper water and/or decreasing levels of oxygen and nutrients, i.e. more distal environments towards the basin interior.
in the caspian Sea (a Paratethyan remnant) which is the best modern analogue of lake Pannon, BooMer et al. (2005) reported a steep gradient in ostracod diversity with increasing water depth within the deep water realm.They found that the number of ostracod species decreased from 17 to 3 between 315 and 479 m. in addition, their samples showed that total specimen abundance declined exponentially with increasing water depth.We speculate that these patterns may be analogous with the diversity and abundance drop that we observed in our samples, although there are no means of estimating the absolute water depth in the early Pannonian TB.

Biostratigraphic interpretation and age
various ostracod biostratigraphic systems have been erected in different parts of the Pannonian Basin System, but they usually reflect local characteristics and significantly differ from each other (e.g.PoKorNý, 1944;KollMaNN, 1960;SoKač, 1972;KrS tiĆ, 1973aKrS tiĆ, , b, 1985;;JiřičeK, 1985;rundiĆ, 1998, 2002, 2006;rundiĆ et al., 2011). ganiĆ et al. (2010) and Ter BorGH et al. (2013) came to the conclusion that the "classical" Lake Pannon ostracod biozones are difficult to identify in the otherwise diverse and abundant ostracod record of the Beočin claypit (Fruška Gora, Serbia), which is roughly coeval with these Transylvanian samples, possibly because earlier biostratigraphic research underestimated the role of palaeoecological conditions in the occurrence and distribution of ostracods.a similar view was expressed by olTeaNu (2011).
as no special zonation for the TB has been currently produced, the biostratigraphic zonation of KrStiĆ (1971KrStiĆ ( , 1972aKrStiĆ ( , b, 1973aKrStiĆ ( , b, 1985) ) and SoKač (1972SoKač ( , 1990) ) originally elaborated for the southern parts of the Pannonian Basin is applied here.recent stratigraphic observations from the TB (WaNeK, 1992a;Fi li PeScu, 1996;FiliPeScu et al., 2011) were also taken into account.For instance, WaNeK (1992b) found that Amplocypris reti culata is probably an endemic species for the TB, and is present only in the "α phase" of PoKorNý (1944), corresponding to the lowermost Pannonian, i.e. lower part of the Slavonian Substage; Loxoconcha rhombovalis determines the final part of the Slavonian Substage; Cyprideis pannonica appears in the uppermost Sarmatian and is present in the "α phase" of the Pannonian.KrStiĆ (1985) erected 8 stratigraphic ostracod zones for the Pannonian Stage: four zones in the older Slavonian and four in the younger Serbian Substages.The four Slavonian zones (from bottom to top) are the Hemicytheria loerentheyi, Hemicytheria hungarica, Hemicytheria tenuistriata, and Propontoniella candeo zones.characteristic species of the three latter zones from the present material include: Hemicytheria hungarica zone: Cyprideis pannonica, Am plocypris reticulata, Amnicythere miscere, Herpetocyprella au riculata, Candona (Caspiocypris) transilvanica.
The appearance of Hemicytheria reticulata in the latter biozone requires some discussion because SoKač (1972) and ol-Plate 1. Pannonian ostracod assemblages from the southwestern part of the TB.
Plate 3. Pannonian micropalaeontological assemblages from the southwestern part of the TB.
TeaNu (2011) claim that this species occurs only in the Serbian substage "Late Pannonian").indeed, the specimens presented here differ from the original description of SoKač (1972) in lacking the sharp, high ventral rib and the pronounced posterioventral part.Such differences in the expression of ornamentation have been extensively discussed (for more details see KeeN, 1982), and they can be related to ecological or genetic factors, especially in the brackish environment of lake Pannon in which ecological conditions were highly variable (PiPíK, 1998).lake Pannon is well known for its extensive intralacustrine evolution (e.g.Geary, 1990;PiPíK 2007).This discovery of H. reticulata may represent an ancestor of H. reticulata in the sense of SoKač (1972), but this relationship should be demonstrated by detailed morphometric and evolutionary study of the subfamily Hemicytherinae in lake Pannon. in conclusion, the three ostracod biozones above are represented in the samples from the southwestern part of the TB (Table 1).Lopadea veche and gârboviţa belongs to the Hemicytheria hungarica zone.Samples from gârbova de Jos, oarba de Mureş, and Mihalţ can be assigned into the Hemicytheria tenuistriata zone.Finally, the ostracod fauna from tău and cunţa indicates the Propontoniella candeo zone.all these zones belong to the lower Pannonian Slavonian Substage, but the oldest Pannonian ostracod biozone, the Hemicytheria loerentheyi zone was not iden tified in any of the samples.this interpretation is roughly supported by the mollusc fauna.The age of the outcrops is thus approximately between 10 and 11.3 Ma (cf. vaSiliev et al., 2010).

Figure 2 .
Figure 2. Lopadea Veche; A -alternation of argillaceous marl and yellowish, fine-and medium-grained sand layers, several cm in thickness.White dot indicates sampling location.B -close-up view of the sampled argillaceous marl.

Figure 1 .
Figure 1.Geological map of the Transylvanian Basin with the distribution of Pannonian sediments and location of the sampled outcrops (adapted from DE LEEUW et al., 2013).

Figure 3 .
Figure 3. Gârbova de Jos; A -alternation of clast-supported, graded conglomerates, pebbly mudstones, and mud-clast conglomerates; the outcrop is cut by a large normal fault.White dot indicates sampling location.B and C -thin bedded turbidites (fine-grained, graded sandstone beds and mudstone with mud clasts).

Figure 4 .
Figure 4. Gârboviţa; A -alternation of marl beds and medium-to very fine-grained, graded sandstone layers.B -close-up view of the marl layers, stained by organic matter.White dot indicates sampling location.

Figure 5 .
Figure 5. Mihalţ.Decimetre to metre thick, massive or laminated marl layers intercalated with thin sandstone beds.White dot indicates sampling location.

Figure 6 .
Figure 6.Tău.An erosional surface divides the outcrop into a lower unit, dominated by mudstones formed as levee to overbank deposits intercalated with rare overspilling thin-bedded turbidites, and an upper unit with the complex, migrational deep-water channel fill.White dot indicate sampling locations within the lower unit.

Figure 8 .
Figure 8. Pie charts of species distribution in each sample (percentage of specimens in all specimens from 250 g sediment).