Paleoenvironmental evolution of the East Carpathian foredeep during the late Miocene–early Pliocene (Dacian Basin; Romania)

Cm

. Ju BdUtr23-25, Bucharest, RO-70318, Romania

a r t i c l e i n f o

Article history:Received 27 May 2011Accepted 12 April 2012Available online 21 April 2012

Keywords:ParatethysCarpathian foredeepbiostratigraphypaleoenvironment

Global and Planetary Change 103 (2013) 135148

Contents lists available at SciVerse ScienceDirect

Global and Plan

l se1. Introduction

The Miocene paleoenvironmental evolution of the Mediterraneanand Paratethys regions is largely inuenced by the opening and clo-sure of the marine connections that strongly regulated the water ex-change between the two domains and with the Indian and Atlanticoceans (e.g. Harzhauser and Kowalke, 2002; Popov et al., 2006;Harzhauser et al., 2007; De Leeuw et al., 2010). This progressively

Paratethys (Peryt, 2006) and the Messinian in the Mediterranean(Hs et al., 1973).

The ParatethysMediterranean water connection during theMessinian is still heavily debated and the location of such a marinegateway has not been proven so far (Popov et al., 2006; Krijgsmanet al., 2010). The present-day connection through the Bosphorus isbelieved to have originated much later in the Pliocene (e.g. agatayet al., 2006), but the presence of many fossils of Paratethyan afnityresulted in restricted conditions, signicant wvelopment of endemic faunas and changes ofthe deposition of massive evaporites durin

Corresponding author. Department of Geology, FacuBucharest University, Blcescu Bd. 1, 010041, Romania.

E-mail address: [email protected] (M. Stoica

0921-8181/$ see front matter 2012 Elsevier B.V. Alldoi:10.1016/j.gloplacha.2012.04.004formed a semi-isolated entity during the Portaferrian and experienced connectivity to the Black Seadomain during the Odessian and Bosphorian.

2012 Elsevier B.V. All rights reserved.MessinianostracodsDacian Basina b s t r a c t

The thick and continuous Mio-Pliocene sedimentary successions of the Focani Depression in the Dacian Basinof Romania provide an excellent opportunity to study the paleoecological changes in the Eastern Paratethysduring the time when the Mediterranean and Black Sea experienced major sea level uctuations related tothe closure and re-opening of the marine connection to the Atlantic Ocean during the Messinian Salinity Crisis.These successions form the basis of high-resolution magneto-biostratigraphic studies that allow a detailedcorrelation to the standard Geological Time Scale. Here, we analyze the paleoenvironmental evolution of theEast Carpathian foredeep by integrating micro- and macropaleontological data and sedimentological analyses.The ostracod andmollusc fossil associations from the Rmnicu Srat river section indicate that the late Maeotiandepositional environment was characterized by shallow waters and littoral to uvio-deltaic sediments. TheMaeotianPontian boundary (6.04 Ma) is marked by a marine ingression, comprising benthic (agglutinatedand calcareous) and planktonic (Streptochilus spp.) foraminifera and nanofossils. Following this marine ingres-sion, the Lower Pontian (Odessian; 6.045.8 Ma) fauna shows an increased bathymetry of the basin. Thepresence of ostracod species with eye tubercles indicates depositional environments within the photic zone(b100 m). The Middle Pontian (Portaferrian; 5.85.5 Ma) is marked by a widespread sea level loweringresulting in dominant uvio-deltaic conditions. This ecostratigraphy demonstrates that the main Messiniansea-level draw down (at 5.65.5 Ma) occurred in mid-Portaferrian times. Paleoenvironmental indicatorsshow that the water level in the Fosani Depression dropped less than 100 m during Mediterranean desiccation.The Dacian Basin remained lled with water, suggesting a positive hydrological balance for the region. This iscompatible with the presence of a shallow barrier at Dobrogea (the Galati passage), separating the DacianBasin from the Black Sea Basin during the lateMiocene. The PortaferrianBosphorian boundary (5.5 Ma) ismarkedby a second transgressive event, but this time without marine foraminifera. We conclude that the Dacian Basinc National Institute of Marine Geology and Geoecology, GeoEcoMar, Dimitrie Onciul StreetPaleoenvironmental evolution of the EastMioceneearly Pliocene (Dacian Basin; Ro

M. Stoica a,, I. Lazr a, W. Krijgsman b, I. Vasiliev b, Da Department of Geology, Faculty of Geology and Geophysics, Bucharest University, Blcescb Paleomagnetic Laboratory Fort Hoofddijk, Utrecht University, Budapestlaan 17, 3584 CD

j ourna l homepage: www.eater level variations, de-salinities, culminating ing the Badenian in the

lty of Geology and Geophysics,Tel.: +40 21 3143508.).

rights reserved.arpathian foredeep during the lateania)

ipa c, A. Floroiu a

. 1, 010041, Romaniaecht, The Netherlands

etary Change

v ie r .com/ locate /g lop lachain the latest Messinian Mediterranean sequences (Esu, 2007) supportthe hypothesis that the Paratethys Sea drained into the Mediterraneanafter its desiccation phase, relling it progressively with brackishwater and resulting in the establishment of Lago Mare facies all overthe Mediterranean Basin (Cita et al., 1978; Cosentino et al., 2006;Orszag-Sperber, 2006). It has also been shown that the water level inthe Black Sea dropped because of Mediterranean desiccation (Dinu etal., 2005; Gillet et al., 2007; Krijgsman et al., 2010; Vasiliev et al.,

2011), indicating that a marine ParatethysMediterranean connectionmust have been present at Messinian times.

In this paper we focus on the thick and continuous sedimentarysuccessions of the Focani Depression, one of the main late Miocenedepocenters in the Dacian Basin of Romania, to investigate thepaleoenvironmental changes in the Eastern Paratethys during theMessinian. We integrate paleoecological information from ostracods,foraminifera andmolluscs with sedimentological analyses and a recent-ly developed chronology (Krijgsman et al., 2010). This allows making adetailed reconstruction of the paleogeographic and paleoenvironmentalevolutions of the East Carpathian foredeep during the late Miocene andearly Pliocene.

2. Geological background

2.1. The Dacian Basin of the Eastern Paratethys

The Paratethys domain (Laskarev, 1924) developed as the northernbranch of the former Tethys Ocean and became progressively separatedfrom the southern Mediterranean branch by ongoing tectonic move-ments in the AfricanEurasian collision process (Fig. 1). The initiationof Paratethys took place 35 millions of years ago, from where it subse-quently evolved as a large intra- and intercontinental marine domainthat extended from the Alps to the Aral Sea (Bldi, 1980; Rusu, 1988;Schultz et al., 2005). Until the Middle Miocene, Paratethys was in com-munication with the normal marine environments of the Mediterra-nean Basin and Indian Ocean. The different Paratethys basins, mainlythe AlpineCarpathian Basin, the Black Sea Depression and the CaspianDepression, were intercommunicating, with periodical phases of isola-tion. By the end of the Middle Miocene (late BadenianSarmatian),

Paratethys communications with the Mediterranean and Indian Oceanwere restricted and eventually closed (Rgl, 1998). Subsequently, Para-tethys itself subdivided into several brackish (Lake Pannon) and low sa-linity restricted marine basins (Eastern Paratethys) during the lateMiocene, all of them developing their own endemic fauna.

The Carpathian orogenwas tectonically uplifted to become a barrierin Sarmatian times (~1112 Ma), separating the Pannonian and Tran-sylvanian Basins of the Central Paratethys from the Dacian and EuxinianBasins of the Eastern Paratethys (Sanders et al., 1999; Cloetingh et al.,2004; Vasiliev et al., 2009). In the Central Paratethys, this resulted in amajor environmental change from marine (Sarmatian) to mainly freshwater environments (Pannonian), recently magnetostratigraphicallydated to take place between 11.6 and 11.3 Ma (Vasiliev et al., 2010;Paulissen et al., 2011; Ter Borgh et al., 2013-this volume; De Leeuw etal., 2013). The Dacian Basin evolved as a separate paleogeographic enti-ty where marine conditions prevailed much longer than in the CentralParatethys (Saulea et al., 1969). This resulted in the confusingnomenclature of a Sarmatian s.l. stage, commonly used in Eastern Para-tethys time scales, which was recently solved by using Volhynian,Bessarabian and Khersonain stages instead (Fig. 1c).

2.2. The Rmnicu Srat section in the East Carpathian foredeep

The Dacian Basin developed as a part of the Eastern Paratethys,located in between the Southern Carpathians, Pre-Balkan area andthe Dobrogean High (Matenco and Bertotti, 2000). The eastern partof the Dacian Basin (called Focani Depression because of its high subsi-dence character) comprises the thickest Neogene sedimentary coverof the Dacian Basin, approaching ~13 km (Tarapoanca et al., 2003).Excellent exposures are on the western ank of the basin along the

ne

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136 M. Stoica et al. / Global and Planetary Change 103 (2013) 135148Miocen

Mediterranean

Paratethys

Fig. 1. Schematic paleogeographic maps of the a) late Eocene and b) late Miocene indicata

b

Late Eoce

Tethys Ocean area in the East Carpathian foredeep. Time scale for the Dacian Basin (after Vasiliev et al., 2c

Paratethys retreat (after Blakey, 2011). The star locates the relative position of the study

004 and Krijgsman et al., 2010) and its relation with the standard GTS.

almost continuously outcropping Putna and Rmnicu Srat river sec-tions (Andreescu and Papaianopol, 1970; Andreescu, 1973, 1975;Andreescu and Ticleanu, 1976; Vasiliev et al., 2004). These sections con-sist in the lower part (Upper BessarabianMaeotian) of alternating shal-low sandstones and shales (Saulea et al., 1969), tilted to near verticalpositions, and in the upper part (Pontian to Romanian) of shales, silt-stones, sandstones and coals (Pana, 1966; Grasu et al., 1999; Panaiotuet al., 2007), progressively less tilted to about 2030E. An extensive net-work of seismic proles shows the absence of large tectonic and erosionalstructures in the basin indicating continuous subsidence and depositionfrom the Upper Bessarabian to Romanian (Fig. 2b; Tarapoanca et al.,2003). Paleomagnetic data furthermore showed that no signicant rota-tions affected the region after the deposition of the Upper Bessarabiansediments (Dupont-Nivet et al., 2005).

The 7.2 km thick Rmnicu Srat river section (Fig. 2c) is excellent-ly exposed and its Maeotian, Pontian and Dacian deposits compriseabundant micro andmacrofossils. The changes in characteristic faunalassemblages allowed the subdivision and correlation to regional EasternParatethys Stages (Maeotian, Pontian, Dacian) and Pontian substages(Odessian, Portaferrian, Bosphorian) according to historic biostrati-graphic denitions (e.g. Stevanovic et al., 1989).

2.3. Biochronology

In the framework of the Dutch research school of Integrated SolidEarth Sciences (ISES), magnetostratigraphic time scales have been

constructed for the sedimentary sequences of the East and SouthCarpathian foredeep (Vasiliev et al., 2004; Vasiliev et al., 2005). Thisresulted in high-resolution chronologies for the Maeotian to Romanian(~8 to ~4 Ma) sediments of the Focani Depression and the GeticDepression (southern Carpathians). The reliability of the magnetic sig-nal has been conrmed by detailed rock magnetic studies, that showedthe presence of two distinctly different types of greigite, a primarymagnetosomal greigite and an early diagenetic (b10 kyr) authigenicgreigite, both providing stable and reliable paleomagnetic directions(Vasiliev et al., 2007; Vasiliev et al., 2008). One problem with thesestudies was that they were lacking direct biostratigraphic control andthat boundary locations from geological maps had to be used to calcu-late the ages for the Paratethys Stage boundaries.

The Eastern Paratethys stages and substages are all represented inthe East Carpathian foredeep and can very well be identied bymeans of their individual ostracod assemblages (Fig. 3, Plates 1, 2).This method allowed determination and magnetostratigraphic datingof the regional stage boundaries in the Rmnicu Srat section(Krijgsman et al., 2010). The MaeotianPontian transition is locatedclose to the top of chron C3An.1n and is thus very accurately datedat 6.040.01 Ma. The OdessianPortaferrian and PortaferrianBosphorian transitions are both located within chron C3r. Their ageshave been determined by assuming constant sedimentation ratesand interpolation of the paleomagnetic age constraints from the re-versal boundaries C3An.1n(y) and C3n.4n(o). This resulted in ages of5.80.1 Ma for the OdessianPortaferrian and 5.50.1 Ma for

) sei

137M. Stoica et al. / Global and Planetary Change 103 (2013) 135148Fig. 2. a) Location of the study area in the Romanian Carpathians, indicated with a star; b

successions from Sarmatian (= Khersonian) to Pleistocene; c) detailed geological map of tsmic section modied after Tarapoanca et al. (2003) indicating continuous sedimentary

he Rmnicu Srat river section (modied after Andreescu and Ticleanu, 1976).

138 M. Stoica et al. / Global and Planetary Change 103 (2013) 135148the PortaferrianBosphorian boundary, respectively. The PontianDacian boundary, and thus also the BosphorianGetian substageboundary, is located within the reversed chron C3n.2r at an age of4.700.05 Ma, in excellent agreement with earlier results fromthe south Carpathian foredeep (Vasiliev et al., 2005; Krijgsman etal., 2010).

3. Paleoenvironmental evolution of the East Carpathian foredeep

3.1. Methods

The Rmnicu Srat river section was investigated in detail for mi-cropaleontological analyses primarily focusing on foraminifera andostracods. In addition, sedimentological and stratonomic investiga-tions have been performed on the MaeotianPontian successions.The sedimentological data coverage is discontinuous, as detailed study lo-cations have been chosen according to outcrop conditions, but additionalobservations have been made on smaller-sized outcrops located in

Fig. 3. Upper Miocene to Lower Pliocene ostracod assemblages and the main paleoenviron(modied after Krijgsman et al., 2010). Salinity and water level curves are schematic interp

Plate 1.Most relevant ostracod species (Superfamily Cypridoidea) from the Upper Maeotianindividuals, external lateral views, LV = left valve, RV = right valve, RM=micropaleontolo2) Candona (Caspiocypris) pontica Soka, carapace, view from RV, RM 207, Lower Pontian; 34) Candona (Typhlocyprella) ankae Krsti, RV, RM 215, Middle Pontian; 5) Candona (Typhltocypria) ossoinaensis Krsti. carapace, view from RV, RM 88, Upper Pontian; 7) Candona negsp., carapace, view from RV, RM 89, Upper Pontian; 9), 10) Candoniella sp., 9) carapace, view(Zalnyi), carapace, view from RV, RM 207, Lower Pontian; 12) Candona (Hastacandona) hytoniella acuminata (Zalnyi), RV, RM 94, Upper Pontian; 14) Pontoniella striata (MandelstamRV, RM 220, Upper Pontian; 16) Zonocypris membranae Stancheva, fragmented LV, RM 215from LV; 18) carapace, view from RV; all specimens from RM 207, Lower Pontian; 19), 20)all specimens from RM 88, Upper Pontian; 21), 22) Cypria sp.; 21) carapace, view from RV;niles), LV, RM 201, Upper Maeotian; 25) Ilyocypris sp., carapace, view from LV, RM 79, UpperRV; RM 88, Upper Pontian.between the main exposures. Samples were processed by standard mi-cropaleontological methods, sieved over sieves of 63 m and hand-picked under a microscope. Macropaleontological analyses on mol-lusks have been performed in less detail. Taxonomic identicationsand ecological inferences were based on Stancheva (1968, 1990);Soka (1972, 1990a, 1990b); Hanganu (1974); Hanganu andPapaianopol (1977; 1982); Krsti and Stancheva (1989); Olteanu(1989, 1995); Papaianopol (1989); Meisch (2000); Gliozzi et al.(2005, 2008); Stoica et al. (2007); Harzhauser et al. (2008); andCziczer et al. (2009).

3.2. The Upper Maeotian

The Upper Maeotian of the Rmnicu Srat river valley is well ex-posed on the outcrops downstream of Jitia village (Fig. 2c). In general,the Upper Maeotian is represented by alternations of sandstone andsilt. Many sandy units display channel structures, and wave ripples arefrequently observed on the upper part of the sandstone beds. Internal

mental settings and events from the Rmnicu Srat valley section of the Dacian Basinretations of the various paleoenvironmental indicators.

and Pontian of the Rmnicu Srat valley section (all valves of ostracods belong to adultgical samples no.); 1. Amplocypris ex. gr. dorsobrevis Soka, LV, RM 215, Middle Pontian;) Candona (Caspiocypris) alta (Zalnyi), carapace, view from RV, RM 88, Upper Pontian;ocypris) sp., carapace, view from the RV, RM 207, Lower Pontian; 6) Candona (Camp-lecta G.O. Sars, carapace, view from RV, RM 87, Upper Pontian; 8) Fabaeoformiscandonafrom RV, 10) LV; all from RM 207, Lower Pontian; 11) Candona (Hastacandona) lotzyisterica Kristi & Stancheva, carapace, view from RV, RM 207, Lower Pontian; 13) Pon-), RV, RM 220, Upper Pontian; 15) Pontoniella quadrata (Krsti), carapace, view from

, Middle Pontian; 17), 18) Candona (Zalanyiella) venusta (Zalnyi); 17) carapace, viewCypria tocorjescui Hanganu; 19) carapace, view from LV; 20) carapace, view from RV;22) carapace, view from LV; RM 207, Lower Pontian; 23), 24) Pseudocandona sp. (juve-Pontian; and 26), 27) Bakunella dorsoarcuata (Zalnyi); 26) LV; 27) carapace, view from

139M. Stoica et al. / Global and Planetary Change 103 (2013) 135148

140 M. Stoica et al. / Global and Planetary Change 103 (2013) 135148

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depsedimentary structures consist of small scale cross-lamination, whichare occasionally disturbed, probably due to the elimination of waterduring sediment compaction. The most valuable paleoenvironmentalsignal comes from the presence of wave rippled sediments, pointingto deposition in shallow water, probably on the lower shoreface.Based on these structures the thick bedded sandy layers are interpretedas shallow water deposits that probably accumulated in the proximityof the river mouth under strong uvial control.

The ostracods are highly abundant but very poor in species number(Figs. 3, 4, Plate 1). The ostracod assemblages consist of several speciesof Cyprideis (Cyprideis pannonica and C. ex. gr. torosa) and some rarecandonids like Pseudocandona sp. (juveniles) and Candoniella sp. Spo-radically, Leptocythere blanda is present.

1 mm

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Clay

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Fig. 4. Stratigraphy, lithology and paleontology of the Upper Maeotian of the Rmnicu Sratassemblage dominated by Cyprideis sp.; c) accumulation of microgastropods (Hydrobia spp.)ex. gr. subrecurvus (Sinzow).

Plate 2.Most relevant ostracod species (Superfamily Cytheroidea) from the Upper Maeotianbelong to adult individuals, external lateral views, LV = left valve, RV = right valve, RM=mRV, RM 116, Upper Maeotian; 2), 3) Cyprideis ex. gr. torosa Sars; 2) smooth specimen, carapPontian; 4), 5) Cyprideis sp. 1; 4) LV; 5) RV; RM 54, Lower Dacian; 6), 7) Cyprideis sp. 2; 6) LLV, male; RM 5, Lower Dacian; 10) Cytherissa sp., LV, RM 79, Upper Pontian; 11) Pontoleberismotasi Olteanu; 12) LV, male; 13) carapace, view from RV, female; RM 220, Upper Pontian; 194, Upper Pontian; 16) Tyrrhenocythere lipescui (Hanganu), LV, RM 88, Upper Pontian; 17)ex. gr. bosqueti (Livental), LV, RM 88, Upper Pontian; 19), 20) Amnicythere cymbula (Liventalgr. cymbula (Livental); 21) LV; 22) RV; RM 207, Lower Pontian; 23), 24) Amnicythere costSchneider; 25) LV; 26) RV; RM 207, Lower Pontian; 27) Leptocythere blanda, LV, RM 215, Up29), 30) Amnicythere andrusovi (Livental); 29) LV; 30) RV; RM 94, Upper Pontian; 31), 32)Maeotocythere bacuana (Livental); 33) LV; 34) RV; RM 220, Upper Pontian; 35), 36) MaeotoLivental, LV, RM 220, Upper Pontian; and 38) Loxoconcha babazananica Livental, RV, RM 96a

1 cmThe dominance of freshbrackish water and littoral conditions isalso shown by the presence of abundant microgastropods likeHydrobiasp. and Teodoxus sp. and Unionidae bivalves Psilunio (Psilunio) ex. gr.subrecurvus (Fig. 4).

The observed macro and micro faunas indicate low salinity(05) environments, typical of littoral setting or within lakesof short life time. In the upper part of the Maeotian, intercalationsof oolitic sandstones with micro-gastropods are common (Fig. 4c,d).

3.3. The MaeotianPontian transition

An important transgressive event takes place at the MaeotianPontian boundary, characterized by a sudden lithological change to

d

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e ripples

tratigraphical ple

Microgastropods (Hydrobia spp., Theodoxus spp.)

Unionids

1 cm

valley section: a) wave ripples on the upper bedding plane of a sand layer; b) ostracod; d) oolite sandstones with abundant gastropods (Theodoxus spp.); e) Psilunio (Psilunio)

, Pontian and Lower Dacian of the Rmnicu Srat valley section (all valves of ostracodsicropaleontological sample no.); 1) Cyprideis pannonica (Mhes), carapace, view fromace, view from RV, RM 114, Upper Maeotian; 3) nodded specimen, RV, RM 226, UpperV; 7) RV; RM 65, Upper Pontian; 8), 9) Cytherissa bogatschovi Livental; 8) LV, female; 9)pontica (Stancheva), fragmented RV, RM 209, Lower Pontian; 12), 13) Tyrrhenocythere4), 15) Tyrrhenocythere ex gr.motasi Olteanu; 14) LV; 15) carapace, view from RV; RMTyrrhenocythere pannonicum (Olteanu), LV, RM 209, Lower Pontian; 18) Maeotocythere); 19) LV; 20) carapace, view from RV; RM 220, Upper Pontian; 21), 22) Amnicythere ex.ata Olteanu; 23) LV; 24) RV; RM 220, Upper Pontian; 25), 26) Amnicythere ex gr. lataper Maeotian; 28) Amnicythere ex. gr. polymorpha Olteanu, LV, RM 219, Upper Pontian;Amnicythere palimpsesta (Livental); 31) LV; 32) RV; RM 207, Lower Pontian; 33), 34)cythere incusa Olteanu; 35) LV; 36) RV; RM 203, Lower Pontian; 37) Loxoconcha petasa, Upper Pontian. (see on page 140)

dominantly silty clays. This event coincides with a short-time replace-ment of the fresherwater fauna by a fauna of signicantly higher salinity.These assemblages are dominated by the occurrence of benthonic calcar-eous foraminifers (species of Ammonia and Porosononion) and especiallyof agglutinated foraminifers (species of Ammotium). The enigmaticplanktonic foraminifera genus Streptochilus has also been observed inlarge numbers at the same level (Fig. 5). The biserial planktonic forami-nifera were earlier described from the Upper Maeotian deposits of theWestern Caucasus as belonging to the genus Bolivina, and some Bolivinaspecies were also reported from the Taman peninsula (Maissuradze,1988). Several morphological species of Streptochilus (Foraminifera)were described in the Miocene of the western Indian Ocean and theeastern Atlantic. They had previously been assigned to the benthicgenus Bolivina, but evidence on their apertural morphology, togetherwith accumulation rate data and isotopic composition shows that theylived as plankton, and should be assigned to the planktic genusStreptochilus (Smart and Thomas, 2006, 2007). It was suggested thatStreptochilus may have evolved polyphyletically, either from biserialplanktic or benthic ancestors, possibly in response to the occurrenceof relatively eutrophic environmental conditions caused by intermittentupwelling, leading to high algal growth rates but low transport efcien-cy of organic matter to the sea oor (Smart and Thomas, 2007). Recentinvestigations of the Upper Badenian and Sarmatian of the Transylva-nian Basin revealed particular, small sized planktonic foraminiferal as-semblages that include also the biserial foraminifera Streptochilusoccurring in relation to a transgressive event close to the end ofBadenian and provide evidence for a paleogeographic connection tothe Indo-Pacic area at that time (Filipescu and Silye, 2008).

Starting with the Pontian, a large diversication of the ostracod faunatook place, marked by a sudden increase of species of Pontoniella andCandona: Pontoniella acuminata, Candona (Hastacandona) lotzy,Candona (Hastacandona) hysterica, Candona (Zalanyiella) venusta,Fabaeformiscandona sp., Candona (Caspiocypris) alta, Candona(Caspiocypris) pontica (Fig. 3, Plate 1). Cyprideis species are still veryfrequent.

The transitional interval is further characterized by shell accumu-lations with the bivalve Congeria (Andrusoviconca) amygadaloidesnovorossica, a biostratigraphic marker for the MaeotianPontianboundary. The association of C. (A) amiygdaloides novorossica, micro-gastropods and unionids (Psilunio sp.) macrofauna is abruptly rep-laced by an association of limnocardiids (Fig. 5), marking the baseof the Pontian according to its original denition.

The MaeotianPontian boundary as dened here, is thus markedby an inux of marine water into the Paratethys, probably comingfrom the Mediterranean or alternatively from the Indian ocean(Krijgsman et al., 2010; Ruban, 2010). After this very rapid marinewater inux, the environment became less saline, as testied by theabundance and diversity of Candoninae in the Lower Pontian.

3.4. The Lower Pontian (Odessian)

As a consequence of the MaeotianPontian transgression, theLower Pontian starts with ne pelitic successions, deposited in deeperwaters (~100150 m). The littoral and uvial facies from the latestMaeotian are replaced by more distal ones; gray marls and clayswith frequent intercalations of ferruginous marls and silts (Fig. 6).

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Fig. 5. Stratigraphy, lithology and paleontology of the MaeotianPontian transition interagglutinated and calcareous benthic foraminifers; b), c) Ammotium sp.; d), e) Ammonia b

Congeria (Andrusoviconca) amygadaloides novorossica Sinzow rich layers.a

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Congeria (Andrusoviconca) amygadaloides novorossica

of the Rmnicu Srat valley section: a) micropaleontological assemblage dominated byarii (Linn); f), g) Porosononion ex. gr. subgranosus (Egger); h), i) Streptochilus sp.; j)l)

An important rejuvenation of the ostracod fauna is observed in theLower Pontian, resulting in colonization by a large number of species:C. (Caspiocypris) alta, C. (Caspiocypris) pontica, Candona (Camptocypria)ossoinaensis, C. (Zalanyiella) venusta, C. (Hastacandona) hysterica,C. (Hastacandona) lotzyi, P. acuminata, Pontoniella quadrata, Pontoniellastriata, Fabaeformiscandona sp., Candona (Typhlocyprella) ankae, Cypriatocorjescui, Cypria sp., Bakunella dorsoarcuata, Cytherissa sp., C. pannonica,Tyrrhenocythere pannonicum, Amnicythere cymbula, Amnicythere ex.gr.,cymbula, Amnicythere costata, Amnicythere andrusovi, L. blanda (Figs. 3,6; Plates 1,2). The presence of ostracods with eye tubercles indicatesthe need of the photic zone for their development, in agreement withthe presence of green charophyta algae in the same samples. At thebase of the Lower Pontian there is a level with pyrite lled ostracods(Fig. 6), which is similarly observed in the Taman Peninsula of Russia(Krijgsman et al., 2010), pointing to large-scale dissoxic conditionsthroughout the Eastern Paratethys.

The Upper Maeotian mollusc fauna is replaced by limnocardiidsbivalves: Paradacna abichi, Pseudoprosodacna littoralis littoralis,Prosodacna sturi, Caladacna steindachneri, Didacna subcarinata,Limnocardium (Tauricardium) subsquamulosum, Monodacna (Pseu-docatilus) pseudocattillus and Congeria zagrabiensis (Fig. 6).

These faunal assemblages indicate that immediately after theshort marine inux, the salinity of the Dacian Basin waters decreased

again because of the high inux of continental waters. The LowerPontian paleoenvironmentwas generally fresh to brackishwith salinitiesof 78 (Fig. 3).

3.5. The Middle Pontian (Portaferrian)

The Middle Pontian represents a regressive phase in the DacianBasin. There are a large number of uvial sandstones (Fig. 7), fossilsoils, coaly clays and even thin coal levels. Rare occurrences of sand-stones with limnocardiids bivalves are found. The sedimentary recordbecomes scarce in fossils, although ostracods and molluscs typicalof shallow water environment (littoral, uvial and even subaeriallyexposed) have been found.

The ostracod fauna is rather scarce if compared with the LowerPontian one (Fig. 3). The Middle Pontian species are represented by:Amplocypris ex. gr. dorsobrevis (a species with robust shell capableof living in littoral environment where sands are deposited in hydrody-namically active regimes), Candoniella sp., Zonocypris membranae(species able to quickly colonize temporary, short-living lakes),Cyprideis ex.gr. torosa (littoral species), Tyrrhenocythere motasi (aspecieswith robust shell capable of living in sandysilty environments).These species are known to adapt rapidly in changing environmentsfrom the lakes located close to rivers, to marshes and lagoons (Plate 2).

Stra

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143M. Stoica et al. / Global and Planetary Change 103 (2013) 1351481 cm

1 mm

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Ps

Con am

Legend:

Marls

Fig. 6. Stratigraphy, lithology and paleontology of the Lower Pontian of the Rmnicu Stions rich in Limnocardiidae shells; c) micropaleontological assemblage from the basal pmarls rich in Paradacna abichi (R. Hoernes); f) Limnocardiids sandstone (Didacna sp., P

Pseudoprosodacna littoralis littoralis (Eichwald).d e

f

h

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rosodacna sp

(Andrusoviconca) aloides novorossica

Paradacna abichi

Congeria rhomboidea

Dreissena spp.

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g

alley section: a), b) dominant marly sediments with thin ferruginous sandy intercala-of Pontian dominated by Candonidae ostracods with carapaces lled with pyrite; d), e)ocatillus sp., Pseudoprosodacna sp.); and g), h) ferruginous sandy layer with abundant

144 M. Stoica et al. / Global and Planetary Change 103 (2013) 135148Subs

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s The molluscan fauna is also rare and represented by fresh waterlacustrine and uvial forms: unioniids Unio (Rumanunio) rumanusand dreiseniids Dreissena polymorpha (Fig. 7). Frequently, planorbidgastropods typical of continental environments (temporary ponds andlakes) have been identied.

These sedimentological and faunistical changes were caused by animportant base level drop from basinal environments to ood plaindeposits. The changes in lithofacies were reected in changes infauna that became taxonomically poorer and have visible effects inthe marginal areas of the basin (Stoica et al., 2007). The faunal assem-blages indicate fresh water environments (04) and a relativelysmall drop (~100 m) of the water level (Fig. 3).

3.6. The Upper Pontian (Bosphorian)

The Upper Pontian deposits accumulated in a more distal setting,where ner, pelitic sediments are alternated with sandy units. Thesene deposits are represented by massive or stratied gray marlsand clays, rich in fossils, alternating with thinner sandstones andshell accumulations (Fig. 8). The Upper Pontian is marked by a gradualupward increase in littoral anduvial deposits, evolving into deltaic anduvial deposits toward the PontianDacian boundary. This is caused bya transgressive episode that marks the base of Upper Pontian.

A new faunal bloom occurs and some of the species common inthe Lower Pontian become dominant again (Fig. 3). Next to the

1cm

Sandstone

Clay

Legend:

Marls

Fig. 7. Stratigraphy, lithology and paleontology of the Middle Pontian of the Rmnicu Srattinental deposits; b)d) layers with abundant Unionidae bivalves: b) Psilunio sp., c), d) Unio(Brusina).c e

1cm

1cm

aLower Pontian species, some new species appear that will continue toexist up to Dacian (Hanganu, 1974; Hanganu and Papaianopol, 1982;Olteanu, 1989, 1995; Stoica et al., 2007). The main ostracod speciesfrom the Upper Pontian of the Rmnicu Sarat Valley are: A. ex. gr.dorsobrevis, C. (Caspiocypris) alta, C. (Camptocypria) ossoinaensis,Candona (Camptocypria) balcanica, C. (Zalanyiella) venusta, P.acuminata, P. quadrata, P. striata, Candona neglecta, Candoniella sp.,Cypria tocorjescui, Cypria sp., B. dorsoarcuata, Cytherissa boghatschovi,C. ex.gr. pannonica, Cyprideis ex. gr. torosa, Cyprideis sp.2, T. motasi, T.ex. gr.motasi, Tyrrhenocythere lipescui, A. cymbula, A. ex. gr. cymbula,A. costata, A. andrussovi, Amnicythere palimpsesta, Amnicythereex. gr. lata, Maeotocythere ex. gr. bosqueti, Maeotocythere bacuana,Maeotocythere incusa, Loxoconcha babazananica, Loxoconcha petasa(Plate 2). Two species of the Amplocypris genus are recorded in theUpper Miocene and Pliocene deposits of the Dacian Basin (Hanganuand Papaianopol, 1977;Olteanu, 1995; Floroiu et al., 2011):A. dorsobrevisSoka and Amplocypris odessaensis Ilnitzkaia. More additional morpho-metric studies (Danielopol et al., 2011a) are needed to nd out whichis the real taxonomic afliation of Amplocypris species in Paratethys.The presence of Leptocytheridae in the Paratethys Neogene is alsoquestioned. Many species formerly attributed to the genus Leptocythereare now re-evaluated and assigned to other leptocytherids generalike Amnicythere, Callistocythere, Euxinocythere, Maeotocythere,Mediocytherideis (Stancheva, 1968; Gliozzi et al., 2005; Boomer etal., 2010). There is still a lack of consensus in the literature on the

b fd

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Biostratigraphical sample

Terrestrial gastropods Coaly clay

Lignite Viviparus spp.

Pseudoprosodacna sp.

Dreissena spp.

Unionids

valley section: a) sandy channel deposits separated by ood plain, lacustrine and con-(Rumanunio) rumanus Tournour; e) Cepaea sp.; and f) Theodoxus (Calvertia) slavonicus

145M. Stoica et al. / Global and Planetary Change 103 (2013) 135148Subs

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sits generic assignment of leptocytherid species (Namiotko et al., 2011) anddetailed comparative morphological studies must be developed for thisgroup of ostracods (Danielopol et al., 2011b).

The bivalves are represented by numerous species that are mostlytypical for brackish waters (Papaianopol, 1989): D. polymorpha,Prosodacana (Prosodacna) mrazeci, Prosodacana (Prosodacna) savae,Prosodacana sturi, Pseudocatillus sp., Plagiodacna sp., C. steindachneri,Limnocardium nobile, Limnocardium sp., D. subcarinata, Lunadacna lunae,Phyllocardium planum giganteum, L. (Tauricardium) subsquamulosum,Limnocardium (Tauricardium) sp. Unio (Rumanunio) rumanus, Congeriabotenica, and Chartoconcha bayerni. (Fig. 8). Gastropods are also abun-dant and among them are: Viviparus acatinoides, Viviparus neumayrineumayri, Lithoglyphus sp., Bulimus (Tylopoma) speciosus, Melanopsis(Melanopsis) decolata, Zagrabica reticulata, Valenciennius annulatus, andValenciennius sp.

Paleoenvironmentally, the base of the Bosphorian corresponds toa second transgressive event in the Dacian Basin, showing a majorfaunal change in the ostracod assemblages and a lithological changeto more basinal sequences. The PortaferrianBosphorian transitionis marked by a second bloom of ostracod fauna that indicate salinitiesof 78 during the Upper Pontian (Fig. 3).

c

f 1cm

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Coal

Lign

Fig. 8. Stratigraphy, lithology and paleontology of the Upper Pontian of the Rmnicu Sratbasinal ne grained sediments at the base of Upper Pontian; b) wave ripples on the upper bec) ostracod assemblage from the basal part of the Upper Pontian marked by the abundancyUpper Pontian; d) Plagiodacna sp.; e), f) Pseudocatillus sp.; g) Chartchoncha bayerni (R. Hoea b4. Discussion

4.1. Dacian Basin water level changes during the late MioceneearlyPliocene

The presence of agglutinated and calcareous foraminifera of ma-rine origin at the MaeotianPontian boundary interval suggests thata major ooding event has taken place in the Dacian Basin by marinewaters, probably by establishing a connection to the Mediterraneanor Indian Ocean. An Odessian transgression has also been recognizedin seismic proles from the western Dacian Basin (Getic Depression)where the Lower Pontian corresponds to a progradationalaggradationalunit developed during rising water levels (Leever et al., 2010). A LowerPontian transgression has further been documented in other Paratethysbasins and is biostratigraphically marked by a migration of faunal ele-ments from the Pannonian Basin (Hungary) into the Eastern Paratethysand by a migration of typical Aegean species into the Black Sea domain(Stevanovic et al., 1989; Popov et al., 2006). In addition, a marine nano-fossil inux, comprising assemblages that are correlative to SubzoneNN11b, has been reported from the MaeotianPontian boundary inter-val in the Dacian Basin (Marunteanu and Papaianopol, 1998). Fossil

d

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y clay

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Viviparus spp.

Pseudoprosodacna sp. Dreissena spp.

Valenciennius anulatus

Limnocardium (Tauricardium) sp..

Pseudocatillus sp. Plagiodacana sp.

valley section; a) the transition from littoral sandy deposits of Middle Pontian to moredding plane of a sandy layer from the Middle PontianUpper Pontian boundary interval;of Tyrrhenocythere spp.; d)i) most abundant mollusc species from the basal part of thernes); h) Limnocardium (Tauricardium) sp.; and i) Valenciennius annulatus Rousseau.

expected to haveuctuated in relation toMessinian paleoclimatologicalchanges.

146 M. Stoica et al. / Global and Planetary Change 103 (2013) 135148assemblages from the Taman Peninsula of Russia show similar marineassociations at the MaeotianPontian boundary interval indicatingthat this transgression extended at least into the eastern part of theBlack Sea Basin (Krijgsman et al., 2010).

A major water-level drop in the Dacian Basin took place duringPortaferrian times (between 5.8 and 5.5 Ma) and resulted in the re-establishment of uvio-deltaic conditions in the Focani Depression.Our paleontological data indicate that depositional environmentswithin the photic zone (b100 m) abruptly change to faunal assem-blages typical of shallow waters (~050 m) and terrestrial environ-ments during the Portaferrian. This implies that only a relativelysmall water level drop has taken place (~100 m) in the Dacian Basinduring the Portaferrian, although the exact amplitude is still a matterof debate. In seismic proles of the western part of the Dacian Basin,the Portaferrian shows mainly progradational units, deposited duringperiods of low water levels (Leever et al., 2010). The correspondingwater level drop is here roughly estimated at a maximum of 200 m,based on the elevation difference between the shelf edges aboveand below the sequence boundary. The other regions of the DacianBasin that developed in water depths of ~100 m in the early Pontianstarted to evolve in deltaic, uvial, lacustrine and/or littoral environ-ments at the beginning of the Middle Pontian. This indicates that thewater level in the entire Dacian Basin dropped during the Porta-ferrian, which would be compatible with the presence of a shallowbarrier at Dobrogea, separating the Dacian Basin from the Black SeaBasin.

The Upper Pontian is marked by a second transgression in the EastCarpathian foredeep. Interpolation assuming constant sedimentationrates suggests that this Bosphorian transgression started at an age of5.50.1 Ma. In thewestern Dacian Basin, seismic proles show a trans-gressive system tract at the base of the Bosphorian as well (Leever,2007). In the Topolog region of the south Carpathian foredeep, the Bos-phorian is found transgressive on Maeotian deposits while the upper-most Maeotian, Odessian and Portaferrian are missing (Stoica et al.,2007; Floroiu et al., 2011). Our detailed micropaleontological studiesshow that the base of the Bosphorian consists of fresh to brackishwater ostracods, indicating a continental origin for this transgression,probably related to a regional climatic change toward a positive hydro-logical balance for the Paratethys region (e.g. Krijgsman et al., 2010).

A Pliocene marine ooding of the Dacian Basin was previouslysuggested based on the Hinova section (western Dacian Basin),which was interpreted to represent the bottom set of a Gilbert fandelta produced by Mediterranean inow water (Clauzon et al., 2005).We have resampled this Hinova section of Clauzon et al. (2005); theirFig. 6 for biostratigraphic dating. Our micropaleontological analysesshow that this section corresponds to the Lower Pontian (6.05.8 Ma),and thus not to the Pliocene, because it comprises the Odessian ostra-cods, C. (Caspiocypris) alta, C. (Camptocypria) balcanica, P. acuminata,P. striata, C. tocorjescui, B. dorsoarcuata, A. andrusovi, Amnicythere sp.,Mediocytherideis sp. and abundant limnocardiid bivalves, especiallyP. abichi. In addition, recent micropaleontological and stratigraphicstudies of the assumed foreset beds (Clauzon et al., 2005) clearly indicatea BadenianSarmatian age for these coarse clastic sediments that aremost likely tectonically tiltedMiddleMiocene alluvial fan conglomerates(Marinescu, 1978; Jipa et al., 2011).

4.2. ParatethysMediterranean connectivity during the late Miocene andearly Pliocene

The Black Sea itself has experienced signicant water levelchanges during the Portaferrian. The sedimentary succession exposedat the Black Seamargin of Russia (TamanPeninsula) shows a conspicuousenvironmental change in Portaferrian, by brackish marls with Pontianfauna indicative of the lower photic zone (50100 m deep) abruptlychanging to condensed coastal sequences of reddish sands, attributed

there to the base of the Kimmerian (= Middle Portaferrian,Our biostratigraphic results suggest that a marine connectionexisted at the MaeotianPontian boundary at 6.05 Ma, evidenced bythe inux of foraminifera in the Dacian Basin. This is further conrmedby earlier observations of a short calcareous nanofossil inux at theMaeotian/Pontian boundary interval (Marunteanu and Papaianopol,1998). According to earlier paleogeographic reconstructions, the mostlikely marine connection is to the Mediterranean (Popov et al., 2006),but the available biostratigraphic data also do not exclude a gatewayto the Indian Ocean (Krijgsman et al., 2010). Our new biochronologyfor the Dacian Basin furthermore shows that the successively youngernanofossil inux at the PontianDacian boundary, previously suggestedto correlate to the Zanclean ooding event of the Mediterranean(Marunteanu and Papaianopol, 1998), is now dated at 4.7 Ma.

5. Conclusions

New biostratigraphic data from the thick and continuous sedi-mentary successions of the Focani Depression are incorporated intoa magnetostratigraphic time frame. The integration of paleoecologicalinformation from ostracods, foraminifera and molluscs with sedimen-tary structures enables detailed reconstructions of the paleogeo-graphic and paleoenvironmental evolutions of the East Carpathianforedeep during the Messinian.

The Upper Maeotian is marked by sedimentary structures that indi-cate the coexistence of uvial and littoral environments. The faunalrecord suggests low salinity (04) environments, typical ofperennial-lake or littoral setting or of temporary lakes and ponds.

An important transgression takes place at the MaeotianPontianboundary, characterized by a short-time paleoenvironmentalchange to signicantly higher salinities (2030). The faunal assem-blages are dominated by the occurrence of benthic (agglutinated andcalcareous) and planktonic foraminifera. It is the rst time that thesehave been observed at the Maeotian/Pontian interval in the DacianBasin, and they indicate an inux of marine waters at 6.05 Ma.

The Lower Pontian starts with ne pelitic sediments, deposited indeeper water, but still within the photic zone. The salinity decreasedto 78 because of a positive water balance determined by theKrijgsman et al., 2010). This indicates that the Black Sea experienceda sea level drop of at least 50100 m as well.

Drilling in the Black Sea Basin (DSDP Leg 42B) had earlier revealeda peculiar sedimentary layer at the Mio-Pliocene boundary, interpretedas shallow, supratidal and intertidal sediments in the otherwise deep-water sequence and as caused by a sudden drastic (~1600m) loweringof the Black Seawater-level (Hs andGiovanoli, 1979). In addition, seis-mic proles of the Black Sea Basin show evidence of deep canyon cut-ting (Dinu et al., 2005; Gillet et al., 2007). This major down dropscenario of the Black Sea implies a negative water budget for the Para-tethys. In contrast, the hydrological balance of the Black Sea basin isalso considered as positive to explain overspilling of Paratethys watersduring the Mediterranean Lago Mare facies (Cita et al., 1978; Esu,2007; Gliozzi and Grossi, 2008). In that scenario it is envisaged thatthe water level of the Black Sea only dropped to the sill height of thepaleo-Bosphorus. The magnitude and, in some cases, even the sign ofthe Paratethys sea or lake level changes during the Messinian are thusstill seriously debated and subject to ongoing controversy.

Paleogeographic data from the Aegean region indicate that no(signicant) gateway existed between Mediterranean and Paratethys(agatay et al., 2006) and that only ephemeral marine incursions tookplace in the Eastern Paratethys during the Mio-Pliocene period(Stevanovic et al., 1989; Marunteanu and Papaianopol, 1998; Popov etal., 2006). Consequently, water level in the Paratethys could behigher inux of continental waters.

Babinszki, E., Mller, P., 2009. Life in the sublittoral zone of long-lived Lake Pannon:

147M. Stoica et al. / Global and Planetary Change 103 (2013) 135148paleontological analysis of the Upper Miocene Szk Formation,Hungary. Internation-al Journal of Earth Sciences (Geologische Rundschau) 98, 17411766.

Danielopol, D.L., Gross, M., Harzhauser, M., Minati, K., Piller, W.E., 2011a. How and whyto achieve greater objectivity in taxonomy, exemplied by a fossil ostracod(Amplocypris abscissa) from the Miocene Lake Pannon. Joannea Geologie und Pala-eontologie 11, 273326.

Danielopol, D.L., Gross, M., Namiotko, T., Minati, K., Piller, W.E., Harzhauser, M., 2011b.Comparative morphology of ostracod Leptocytheridae a prospect for better un-derstanding the origin and evolution of selected Amnicythere taxa in long-livedLake Pannon (late Miocene). Joannea Geologie und Palaeontologie 11, 5052.

De Leeuw, A., Bukowski, K., Krijgsman, W., Kuiper, K.F., 2010. Age of the Badenian sa-linity crisis: impact of Miocene climate variability on the Circum-Mediterraneanregion. Geology 38, 715718.

De Leeuw, A., Filipescu, S., Matenco, L., Krijgsman, W., Kuiper, K., Stoica, M., 2013. Pa-leomagnetic and chronostratigraphic constraints on the evolution of the Middle The Middle Pontian shows a base level drop with visible effects inthe marginal areas of the basin. It is scarce in fossils, and mainly os-tracods and molluscs typical of shallow and fresh water (04) la-custrine environments have been found, species known to adaptrapidly to changing environments from lakes located close to rivers.

The Upper Pontian deposits accumulated in a more distal setting,with ner pelitic sediments, alternated with sandy units. Theupper part is marked by an increase in littoral and uvial deposits,evolving into deltaic and uvial deposits (salinity between 7 and8) toward the PontianDacian boundary as a consequence of pro-gressive basin lling with sediments.

Acknowledgments

We thank especially Georghe Popescu for his help with bio-stratigraphical analyses of the Rmnicu Srat data (foraminifera). Weacknowledge the constructive comments of Oleg Mandic and twoanonymous reviewers. This work was nancially supported by theNetherlands Research Centre for Integrated Solid Earth Sciences(ISES) and the Netherlands Geosciences Foundation (ALW) withsupport from the Netherlands Organization for Scientic Research(NWO). This research was also supported by CNCSIS Romaniafunding (ID 960 and 1 Euroc).

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Paleoenvironmental evolution of the East Carpathian foredeep during the late Mioceneearly Pliocene (Dacian Basin; Romania)1. Introduction2. Geological background2.1. The Dacian Basin of the Eastern Paratethys2.2. The Rmnicu Srat section in the East Carpathian foredeep2.3. Biochronology

3. Paleoenvironmental evolution of the East Carpathian foredeep3.1. Methods3.2. The Upper Maeotian3.3. The MaeotianPontian transition3.4. The Lower Pontian (Odessian)3.5. The Middle Pontian (Portaferrian)3.6. The Upper Pontian (Bosphorian)

4. Discussion4.1. Dacian Basin water level changes during the late Mioceneearly Pliocene4.2. ParatethysMediterranean connectivity during the late Miocene and early Pliocene

5. ConclusionsAcknowledgmentsReferences