Earth and Planetary Science Letters 290 (2010) 183–191

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Earth and Planetary Science Letters

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Rise and fall of the Paratethys Sea during the Messinian Salinity Crisis

W. Krijgsman a,⁎, M. Stoica b, I. Vasiliev a, V.V. Popov c

a Paleomagnetic Laboratory ‘Fort Hoofddijk’, Utrecht University, Budapestlaan 17, 3584 CD, Utrecht, The Netherlandsb Department of Palaeontology, Faculty of Geology and Geophysics, University of Bucharest, Bălcescu Bd. 1, 010041, Romaniac VNIGRI, All-Russia Petroleum Research Exploration Institute, St. Petersburg, Russia

⁎ Corresponding author. Tel.: +31 30 2531672.E-mail address: krijgsma@geo.uu.nl (W. Krijgsman).

0012-821X/$ – see front matter © 2009 Elsevier B.V. Adoi:10.1016/j.epsl.2009.12.020

a b s t r a c t

a r t i c l e i n f o

Article history:Received 9 July 2009Received in revised form 16 November 2009Accepted 8 December 2009Available online 3 January 2010

Editor: P. DeMenocal

Keywords:ParatethysMediterraneanMessinian Salinity Crisismagnetostratigraphyfloodingsea level change

Extremely thick evaporite units were deposited during the so-called Messinian Salinity Crisis (MSC: 5.96–5.33 Ma) in a deepMediterranean basin that was progressively disconnected from the Atlantic Ocean. A crucial,but still poorlyunderstood component inMessinian evaporitemodels is the connectivity betweenMediterraneanand Paratethys, i.e. the former Black Sea domain. Inadequate stratigraphic correlations and insufficient agecontrol for Paratethys sediments have so far hampered a thorough understanding of hydrological fluxes andpaleoenvironmental changes. Here, we present a new chronology for the Eastern Paratethys by integratingbiostratigraphic and paleomagnetic data fromMio–Pliocene sedimentary successions of Romania and Russia.Weshow that amajor flooding event from theMediterranean surged the Paratethys basins at theMaeotian–Pontianboundary, 6.04 million years ago. This indicates that sea level in both Mediterranean and Paratethys was high atthe beginning of theMSC.We argue in favor of changes in Paratethys–Mediterranean connectivity to initiate theMSC in combination with elusive tectonic processes in the Gibraltar arc. A subsequent fall of Paratethyan waterlevel closely coincides to the Mediterranean isolation-event, corresponding in age to the glacial cycles TG12–14(5.60–5.50 Myr). In the latest Messinian, a major climate change towards more humid conditions produced apositive hydrological balance and likely a transgression in the Paratethys, although our stratigraphic resolutioncannot exclude a possible relation to the Pliocene flooding of the Mediterranean here.

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1. Introduction

Major sea level fluctuations, causing dramatic paleoenvironmentalchanges and related mass-extinctions, form an intricate part of Earthhistory (Hallam and Wignall, 1997). Renowned examples are thebiblical flood of Noah and the Messinian Salinity Crisis (MSC) of theMediterranean. Geological investigations indicated that a great delugesurged the Black Sea basin roughly 8000 years ago, rapidly raising thelake level by some 100 m (Ryan et al., 1997, 2003) so that civilizationsand populations inhabiting the Black Sea shores may have suddenlydrowned (Ryan and Pitman, 1998). The sudden influx hypothesis ishighly debated between geologists and archeologists (Aksu et al., 2002),but may also have occurred in late Messinian times (Hsü and Giovanoli,1979) when the Black Sea domain was part of the Eastern Paratethys(Fig. 1). During the Messinian (7.24–5.33 Ma), the Mediterraneanbecame progressively isolated from the Atlantic Ocean, triggeringwidespread precipitation of gypsum (5.96–5.6 Ma), massive saltdeposition (5.6–5.5 Ma), and a dramatic sea level lowering followedby brackish water environments of “Lago-Mare” (Lake Sea) facies (e.g.Hilgen et al., 2007; Krijgsman and Meijer, 2008; Roveri et al., 2008). Acatastrophic re-flooding from the Atlantic at the beginning of the

Pliocene (5.33 Ma) abruptly ended the salinity crisis by re-establishingopen marine conditions in the Mediterranean (Hsü et al., 1973).

The hydrological flux from Paratethys to Mediterranean is a crucialcomponent in quantitative studies on paleocirculation patterns andprecipitation models of evaporites (Meijer and Krijgsman, 2005;Flecker and Ellam, 2006), but connectivity between the two basins iscontroversial (Çagatay et al., 2006). Overspilling of Paratethys watersinto the Mediterranean has been argued to explain the presence ofbrackish water fauna in the Lago-Mare sediments (Cita et al., 1978),but a lowering of Paratethys levels during the Messinian event is alsosuggested (Hsü and Giovanoli, 1979). Seismic profiles of the Black Seabasin show evidence of deep canyon cutting, but the exactstratigraphic position differs; at the base of the Pontian Stage (Dinuet al., 2005) or intra-Pontian (Gillet et al., 2007). Sequencestratigraphic interpretations on a seismic transect from the westernDacian Basin also reveal significant sea level changes within thePontian Stage (Leever et al., 2009). Seismic and borehole data fromthe Pannonian Basin show unconformities as well, but these areinterpreted to have a regional tectonic origin and no relation toMessinian drawdown (Magyar and Sztanó, 2008). A concurrent baselevel drop has been proposed for the Caspian Sea (Reynolds et al.,1998; Popov et al., 2006), although numerical ages are poorly defined.

Paratethys time scales comprise regional stages (e.g. Maeotian–Pontian–Dacian or Kimmerian within the Mio–Pliocene interval) andsubstages (e.g. Odessian–Portaferrian–Bosphorian within the Pontian)

Fig. 1. Paleogeographic map of the Mediterranean and Paratethys during the Messinian Salinity Crisis interval. Stars indicate locations of the sections and research areas. In theDacian Basin, RS and PU=Râmnicu Sarat and Putna sections are located in the east Carpathian foredeep and TP=Topolog region is in the south Carpathian foredeep. In the Black Seabasin, ZR = Zheleznyi Rog section is located on the Taman Peninsula of the Russian Black Sea margin; SC = South Caspian Basin— Azerbaijan. Triangles locate astronomically datedMediterranean MSC sections (see Hilgen et al. (2007) and Krijgsman and Meijer (2008) for details).

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based on endemic ostracod andmollusc species. At present, correlationsto the marine record are mainly tentatively based on rare incursions ofnannofossils (e.g. Marunteanu and Papaianopol, 1998) and chronos-tratigraphic resolution is generally inadequate to determine causalrelationships with the Mediterranean MSC events.

Here, we construct a robust biochronologic framework for theParatethys domain by integrating paleomagnetic data with detailedpaleontologic analyses of endemic Paratethys faunal (molluscs andostracods) assemblages from sections of the Dacian and the Black Seabasin (Fig. 1). The integrated stratigraphic results of these individualdomains will unfold the intrinsic paleoenvironmental evolution of theEastern Paratethys during the Messinian Salinity Crisis with revisedchronologic constraints.

2. Sections and setting

Paleomagnetic studies recently showed that excellent biochrono-logical control for the Paratethys can be obtained from continuoussedimentary sequences (Vasiliev et al., 2004, 2005). The Dacian Basinin particular comprises several complete and well-exposed sedimen-tary successions from the Pontian Stage, consisting of fossiliferous siltsand sands indicative of lacustrine and fluvio-deltaic environment(Panaiotu et al., 2007). These sediments accumulated rapidly in aforedeep setting, providing a thick continuous exposure of the MSCinterval (Vasiliev et al., 2004). The Râmnicu Sărat and Putna sections(Fig. 1) were shown to carry a primary magnetic signal produced bygreigite magnetofossils, providing reliable records of ancient geo-magnetic field variations (Vasiliev et al., 2008) thus allowing excellentcorrelations to the standard Geological Time Scale (GTS) and tomagnetostratigraphically dated sections in the south Carpathianforedeep (Fig. 1; Vasiliev et al., 2005). It showed that the majorpaleoenvironmental changes in the late Miocene and Pliocene weresynchronous within the Dacian Basin, although these magnetostrati-graphic studies were lacking direct biostratigraphic control. Here wepresent a detailed ostracod biostratigraphy for the Râmnicu Săratsection in the east Carpathian foredeep, one of the most continuous

successions covering the MSC interval, and integrate the results withthe magnetostratigraphic data (Vasiliev et al., 2004, 2007).

The target section in the Black Sea Basin is on Taman Peninsula(Russia); the classic Zheleznyi Rog (Iron Cape) section is 500 m longand covers ∼5 Myr of sediments (Fig. 1). The section has beenextensively studied by several Russian research teams (Semenenko,1979; Trubikhin, 1986; Filippova, 2002), but despite the presence ofpaleontological, paleomagnetic and (K–Ar) isotopic data, correlationsto the GTS are still highly debated (Chumakov et al., 1992; Pevzneret al., 2003; Popov et al., 2006). We have focused here on the Mio–Pliocene interval of the Zheleznyi Rog section and resampled theuppermost Maeotian, Pontian and the lower Kimmerian for paleo-magnetic and biostratigraphic purposes to establish direct correla-tions to the integrated stratigraphic record in the Dacian Basin.

3. Paleomagnetic results

Standard paleomagnetic measurements have been performed toestablish a new magnetostratigraphic record for the Zheleznyi Rogsection (Fig. 2). Thermal (TH) demagnetization was applied withsmall temperature increments of 10–30 °C up to a maximumtemperature of 580 °C in a magnetically shielded furnace. AlternatingField (AF) demagnetization was performed with small field incre-ments, up to a maximum of 100 mT, using an in-house built robotizedsample handler controller attached to a horizontal 2G Enterprises DCSQUID cryogenic magnetometer. Demagnetization results wereanalyzed using orthogonal plots and stereographic projections. Thedirection of the NRM components was calculated by principal-component analysis. Dual polarity components were isolated inmost samples between the 270–420 °C (Fig. 2A–C) or 20–45 mTdemagnetization steps (Fig. 2D,E). Several specimens were demagne-tized up to 580 °C or 100 mT (Fig. 2F). We recognized three polarityintervals in the studied succession, normal polarities at the basal(upper Maeotian) part, reversed polarity in the middle (Pontian) partand normal polarity in the upper (lower Kimmerian) part.

An alternating gradient magnetometer (Princeton Measure-ments Corporation, MicroMag Model 2900 with 2T magnet, noise

Fig. 2. Demagnetization results from the Zheleznyi Rog section. In the Zijderveld plots (A–F), red numbers represent the temperature steps in °C for the TH demagnetization (A–C,F),and blue numbers indicate the field steps in mT for AF demagnetization (D–E). Down-right are the stratigraphic levels in meters. The diagrams are presented with tectonic tiltcorrection (th/tc or af/tc). The red (blue) lines indicate the ChRM direction from the TH (AF) demagnetization. The red circles and the blue diamonds are the symbols used in Fig. 4.Representative first order reversal curves diagrams (G, H) have contours closing around a single domain (SD) peak at Bc=40–50 mT, indicative for greigite as magnetic carrier.

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level 2×10−9 Am2) was used to measure first order reversal curves(FORC) diagrams. The domain state, and particularly the amount ofmagnetic interaction emerges clearly from FORC diagrams. Contoursclosing around a single domain (SD) peak at Bc=40–50 mT (Fig. 2G,H)are similar to those previously reported for greigite in the Dacian Basin(Vasiliev et al., 2007).

4. Rise in Paratethyan water level at theMaeotian/Pontian boundary

The Paratethyan ostracod distribution in Mio–Pliocene timesreflects evolutionary trends, but also the influence of paleoenviron-mental changes. Changing the connectivity with the open oceaninfluences the bathymetry and salinity of Paratethyan basins, which isreflected in the marginal faunal assemblages of the Dacian Basin. Wepresent here the results of a detailed micro-paleontological study,focussing mainly on ostracods and foraminifera of the Râmnicu Săratsection, which provides a high-resolution biochronology for theEastern Paratethys (Fig. 3).

Our biostratigraphic results show that the fossil ostracod assem-blages from the upperMaeotian (Moldavian substage) comprise a lownumber of species, of which Cyprideis pannonica is common andParacandona albicans and Leptocythere blanda are rare (Fig. 3). Thesefossil assemblages are indicative of sub-littoral fresh- to brackishwater environment, suggesting that the upper Maeotian sediments inthe east Carpathian foredeep are associated with temporary lakes onflood plain areas. The marginal areas of the Dacian Basin thus evolvedin almost freshwater conditions, while the paleoenvironment wasdominated by littoral and fluvial conditions.

The Maeotian assemblages are rapidly replaced by lower Pontian(Odessian/Novorossian) associations (Fig. 3). The lower Pontianostracod assemblages indicate relatively deep basinal environments,and a widespread rise of relative sea level. At this time, characteristiclayers formed comprising monospecific Congeria novorossicamolluscs(Stevanovic et al., 1989). Our detailed study of the Maeotian–Pontiantransition interval, for the first time, reveals the presence of

agglutinated and calcareous benthic foraminifera and planktonicforaminifera (Streptochilus and Tenuitellina species) of marine originin the Upper Miocene of the Eastern Paratethys (Fig. 4A–J). Thisindicates that a major marine deluge took place by re-establishing aconnection through theMediterranean to the Atlantic, or alternativelyto the Indian Ocean. Magnetostratigraphic results show that thisflooding interval occurred synchronously in the Dacian and Black Seabasins near the paleomagnetic reversal C3An.2n(y), and is dated at6.04 Ma (Fig. 4). The marine environment in the Eastern Paratethyswas only a short-lived feature of maximum 10 kyr, after which micro-paleontological assemblages are again dominated by ostracodsindicative of brackish water conditions. After this transgressiveinterval, the lower Pontian ostracod fauna reacted to the changes inbathymetry and salinity, while variations in interbasinal connectivityallowed migration of species. It generated a “bloom” of ostracodspecies in the Odessian at ∼5.95 Ma (Fig. 3), especially in thepredominantly pelitic deposits that are well-developed in lowerPontian times.

A transgression at the Maeotian/Pontian boundary has previouslybeen documented from wells and seismics in the western DacianBasin (Jipa, 1997; Leever, 2007; Leever et al., 2009) and isbiostratigraphically marked by a migration of faunal elementsfrom the Pannonian basin (Hungary–Austria) into the EasternParatethys and by migration of typical Aegean species into the BlackSea domain. This is supported by earlier observations of a shortcalcareous nannofossil influx at the Maeotian/Pontian boundaryinterval (Marunteanu and Papaianopol, 1998). Biostratigraphic datafrom the Caspian Basin in Azerbaijan reveal similar changes in faunalelements indicating that this event extended into western Asia(Stevanovic et al., 1989).

5. Fall in Paratethyan water level during the Portaferrian

A marked paleoenvironmental change occurs at the middle Pontian(Portaferrian) of the Dacian Basin. The study region in Romania shows atransition to more sandy facies, with ample presence of wave rippled

Fig. 3. Ostracod distribution of the Râmnicu Sărat section in the east Carpathian foredeep of theDacian Basin. Themagnetostratigraphic pattern is after Vasiliev et al. (2004) and correlatesexcellently to the GTS. It allows high-resolution dating of the ostracod assemblages and related stages and substages. The resulting new ages of the (sub)stage boundaries are indicated.

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sediments indicating deposition in shallow water, probably on thelower shore face (Panaiotu et al., 2007). The Portaferrian thusrepresents a regressive event where the bathymetry of the Dacian

Basin decreased. In marginal settings, the rich Odessian ostracod faunaindicative of basinal conditions is replaced by littoral, fluvial andlacustrine Portaferrian species: Amplocypris dorsobrevis, C. pannonica,

Fig. 4.Detailed integrated stratigraphicdata of theMaeotian/Pontian interval. Pontian–Kimmerianare regional stagesof theBlackSeaBasin.Magnetostratigraphicdata fromRâmnicuSăratare after Vasiliev et al. (2004), fromZheleznyi Rog of this paper. Red circles represent reliable directions from thermal demagnetization,whereby small circles denote greigite, large circlesmagnetite. The bluediamonds indicate directions fromalternatingfielddemagnetization .TheMaeotian–Pontian boundary interval ismarkedbya short influxofmarine calcareousbenthicforaminifera (A–C) Porosononian ex. gr. subgranosus (Egger), (D) Ammonia ex. gr. beccarii (Linné), agglutinated foraminifera, (E,H) Ammotium sp. and planktonic foraminifera comprisingStreptochilus sp. (I–J).

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C. sp., Tyrrhenocythere ex. gr. motasi, Candoniella sp., and Zonocyprismembranae (Fig. 3).

The Portaferrian low-stand is determinedmagnetostratigraphically inthe middle part of chron C3r, and precize ages can thus not be obtainedhere. Assuming constant sedimentation rates for the Râmnicu Săratsection results in interpolated ages of∼5.8 and∼5.5 Ma for the lower andupper Portaferrian boundary, respectively (Fig. 3). Seismic data from thewestern part of the Dacian Basin confirm a general regressive middlePontian low-stand (Leever et al., 2009), while an erosional unconformityof regional significance has been observed between Maeotian and upperPontian sediments at marginal regions (Stoica et al., 2007).

The section at the Black Seamargin shows a conspicuous change atthe top of this interval by deep lacustrine brackish marls with Pontianfauna indicative of the photic zone (b100 m deep) abruptly changingto condensed coastal sequences of reddish sands, with some minorsedimentary hiatuses, attributed to the base of the Kimmerian (Fig. 5).This red sequence comprises oolites/pisolites plus nodular marls thatsuggest high-energetic coastal environments (Fig. 5E). It furthermorecontainsmolluscs that are characteristic of the Portaferrian (Fig. 5F–H)andminerals indicative of evaporitic conditions (selenite, gypsum andjarosite), which probably formed after deposition (Fig. 5I–L). Thisindicates that the Black Sea experienced a sea level drop of about 50–100 m at the base of the Kimmerian (middle Portaferrian), which is

coeval to the intra-Pontian unconformities observed in seismic profilesof the Romanian Black Sea margin (Gillet et al., 2007).

The Caspian Sea may have become isolated during this period, assuggested by the expansion of the deltaic systems of the ‘ProductiveSeries’, which are Kimmerian in age. This is the main hydrocarbonreservoir unit of the South Caspian Basin, thought to represent thelow-stand wedge of a dramatic sea level fall (Hinds et al., 2004). Atentative link has beenmade with the lateMessinian eustatic sea levelfall (Reynolds et al., 1998), but other studies have suggested a relationto large scale plate-tectonic processes (Allen et al., 2002). The base ofthe Productive Series is radiometrically dated at ∼5.5 Ma and isinterpreted as the sudden southward expansion of the Miocene Volgadelta resulting from a major regression (Dumont, 1998).

Consequently, we conclude that all regions in the Eastern Paratethysshowevidence for amarked sea level lowering of at least 50 mduring theMessinian (5.6–5.5 Myr) time interval, corresponding to the Portaferrianof the Dacian Basin and the lowermost Kimmerian of the Black Sea andCaspian basins.

6. Paratethys transgression during the Bosphorian

The upper Pontian (Bosphorian) corresponds to a second transgres-sive event in the Dacian Basin, showing a major faunal change in the

Fig. 5. A) The reddish interval of the Zheleznyi Rog section. Portaferrian molluscs found in the marl interval below the red unit; B) Valenciennius sp., C) Paradacna abichi, D) Dreissenarostriformis. Characteristic mollusc species and the most relevant evaporitic minerals found in the reddish interval, marking the beginning of the Kimmerian: E) oolithic/pisolithicsandstone, F) Caladacna steindachneri, G) D. rostriformis, H) Pteradacna edentula, I) jarosite, J) prismatic gypsum crystals, K) jarosite, and L) radial gypsum. The corresponding levelsare indicated right of the schematic lithological column.

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ostracod assemblages (Fig. 3) and a lithological change to more basinalsequences (Jipa, 1997). The Portaferrian–Bosphorian transition ismarked by a second bloom of ostracod fauna, and most Pontian speciesare well represented. Some species pass through the limit with lowerDacian (Getian substage).

Interpolation assuming constant sedimentation rates, suggeststhat this upper Pontian transgression started at an age of 5.5±0.1 Ma(Table 1). Detailed micropalaeontological studies have not revealedthe presence of marine foraminifera here. In thewestern Dacian Basin,seismic profiles also show a transgressive system tract at the base ofthe Bosphorian (Leever et al., 2009). In the Topolog region of the southCarpathian foredeep, the Bosphorian is found transgressive onMaeotian deposits while the upper Maeotian and lower-middlePontian are missing (Stoica et al., 2007). In addition, the bottom setsof a ‘Gilbert fan delta’ are correlated to this sea level rise (Clauzonet al., 2005), although stratigraphic data from Romanian geologistsindicate that these fan deposits are of pre-Maeotian age (Savu andGhenea, 1967; Nastaseanu and Bercia, 1968).

In the Black Sea Basin, theMiocene–Pliocene boundary is commonlyplaced at the Pontian/Kimmerian boundary. This is in slight disagree-ment with our stratigraphic results, which shows that the red level ofthe lowermost Kimmerian corresponds to the Portaferrian of the Dacian

Table 1New magnetostratigraphic ages for the (sub)stage boundaries in the Dacian and BlackSea basins of the Eastern Paratethys.

Dacian Basin Black Sea Basin

Boundary Age(Ma)

Boundary Age(Ma)

Pontian/Dacian 4.70±0.05 × ×Portaferrian/Bosphorian 5.5±0.1 Portaferrian/Kimmerian 5.6±0.1Odessian/Portaferrian 5.8±0.1 Novorossian/Portaferrian 5.8±0.1Maeotian/Pontian 6.04±0.01 Maeotian/Pontian 6.04±0.01

Basin and thus to the latest Miocene (Fig. 4). Faunal elements ofKimmerian marls, overlying the reddish interval at Zheleznyi Rog, aresimilar to the Bosphorian and can be largely attributed to the Pliocene.The “Productive Series” of the CaspianBasin are also biostratigraphicallydated asKimmerian in termsof Eastern Paratethyan chronostratigraphy(Nevesskaya et al., 2002). The numerical age is still a matter of debate,because of conflicting paleomagnetic evidence on which calibration tothe global record is based, and because biostratigraphic control forinterregional correlation is hindered by the presence of mostly localfaunas and by massive reworking (Jones and Simmons, 1996).

Our integrated stratigraphic results from the Dacian Basin showthat the Pontian/Dacian boundary is younger than the Sidufjall normalchron (C3n.3n) and is magnetostratigraphically dated at ∼4.7 Ma(Fig. 3). This is significantly younger than presumed in otherParatethys time scales, where the Pontian–Dacian stage boundary istentatively positioned at, or close to, the Miocene–Pliocene boundary(5.33 Ma) (Steininger et al., 1996; Clauzon et al., 2005; Snel et al.,2006). It is clear that different definitions have been used for theupper Pontian boundary in Romanian and Russian literature (Fig. 6;Table 1), which is especially problematic when working on the Mio–Pliocene sedimentary successions and seismic sequences of the BlackSea domain. A formal re-definition of the Paratethys regional stagesaccording to international stratigraphic codes is urgently required.

7. Causes and consequences for the Messinian Salinity Crisis

Our new chronological framework for the Eastern Paratethysallows high-resolution correlations with the oxygen isotope curves(Hodell et al., 2001; Hilgen et al., 2007) and the Messinian successionsof the Mediterranean (Fig. 6). These are subdivided into threeastronomically dated evaporite phases; M1) marine “Lower Gypsum”

(5.96–5.6 Ma), M2) halite and resedimented evaporites (5.6–5.5 Ma),M3) Lago-Mare sediments with gypsum (5.5–5.3 Ma) (Krijgsmanet al., 1999; Hilgen et al., 2007; Roveri et al., 2008).

Fig. 6. A new chronology for the different local and regional stages of the Paratethys allows detailed correlations to the GTS, the Mediterranean event stratigraphy during theMessinian Salinity Crisis (M1–M3) (Krijgsman et al., 1999; Roveri et al., 2008) and to the oxygen isotope curves of the Atlantic margin of Morocco (Hilgen et al., 2007). Red star/foraminifer indicates influx of marine nannofossils (Marunteanu and Papaianopol, 1998)/foraminifera (see Fig. 4). Schematic cross-sections show the changes in connectivity andthe phases of basin isolation of the Paratethys and Mediterranean during the Messinian Salinity Crisis.

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7.1. The onset of “Lower Gypsum” formation in the Mediterranean

Our new data shows that the onset of the Messinian Salinity Crisisin the Mediterranean was directly preceded by the marine flooding ofthe Eastern Paratethys, confirming the hypothesis that the LowerGypsum units formed during a relative high-stand of Mediterraneansea level (Flecker et al., 2002; Krijgsman and Meijer, 2008). Atransgression at the onset of the Messinian evaporite formation is inserious contrast to hypotheses inferring glacio-eustatic sea levellowering (Hsü et al., 1973; Clauzon et al., 2005), but has earlier beensuggested on the basis of strontium isotope models (Flecker et al.,2002; Flecker and Ellam, 2006). It is interesting to note that the bloomof Odessian ostracods (Fig. 3), indicating re-stabilization of paleoen-vironmental conditions in the Paratethys, coincides with the onset ofMSC evaporites at 5.96 Ma in the Mediterranean (Krijgsman et al.,1999). Consequently, the changes in Paratethys–Mediterraneanconnectivity at the Maeotian–Pontian transition interval probablygenerated a new hydrological equilibrium in both Paratethys andMediterranean that allows gypsum to precipitate during astronom-ically-forced optimum (=dry) climate conditions on a precessionalresolution in the Mediterranean Basin (Krijgsman et al., 2001).

A flooding of the Paratethys basin could only have happened if itswater levelwas significantly belowglobal oceanandMediterranean level.This indicates that the hydrological budget for the Paratethys region inMaeotian times was slightly negative. Establishing a Mediterranean–

Paratethys connectionwould result in an increased hydrological flux intothe Paratethys and consequently an increase in water and salt flux fromthe Atlantic into the highly restricted evaporation-dominated Mediter-ranean. We speculate that creating a connection to the Paratethys willincrease Mediterranean stratification and ultimately influence thehydrodynamics of the Gibraltar gateways, two crucial factors to explainthe onset of widespread gypsum deposition during the MSC (Meijer andKrijgsman, 2005).

7.2. Location of Paratethys flooding

Another intriguing question is: where did the Paratethys floodingactually come from? The Aegean region of the Mediterranean Sea isthe most likely source area according to the paleogeographicreconstructions of the Paratethys domain (e.g. Popov et al., 2006),although we cannot exclude the Indian Ocean on the basis of our data.A flooding event is further expected to leave marked traces ofsignificant erosion on land and offshore the Bosporus region (e.g.Loget et al. 2005). The Karadeniz-1 borehole in the European part ofthe Turkish Black Sea shelf indeed showsMessinian erosional surfaces(Gillet et al., 2007), which can possibly be traced to the Karacaköyregion at the Black Sea margin northwest of Istanbul. We thusconsider a Karacaköy–Karadeniz passage as potential candidate toaccount for the flooding event, but more detailed biostratigraphic datais necessary to confirm this hypothesis.

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7.3. Down drop of the sea level during the MSC

The observed fall in Paratethyan water level at the base of thePortaferrian is estimated to have occurred at 5.8 Ma in the DacianBasin (Fig. 3). This is remarkably close to glacial peaks TG22–20(Fig. 6), which are suggested to have caused a significant drop inglobal sea level (Shackleton et al., 1995). In the Zheleznyi Rogsuccession this interval also shows evidence of sea level lowering,expressed by the occurrence of white shell beds of Portaferrian age(Po2: Popov et al., 2006).

The climax of the Messinian Salinity Crisis occurred during glacialpeaks TG12–14, when the water exchange with the Atlantic becamerestricted resulting in the formation of massive halite in the deepestparts of the Mediterranean and a dramatic fall in water level (Fig. 6).The potential connection to Paratethys thus also would have becomelost, lowering the water level in the Black Sea Basin immediately tothe level of the paleo-Bosphorus. Our data from Zheleznyi Rog suggestthat this event is clearly reflected in the sharp transition to the reddishinterval at the Russian Black Sea margin of the Taman Peninsula. Theultimate lake levels in the isolated Dacian, Black Sea and Caspianbasins will obviously be influenced by astronomically inducedchanges of regional climate. Depending on the hydrological budgetof the individual Paratethys basins desiccation (negative) or overflow(positive) will take place (Fig. 6).

A marked change occurs in the oxygen isotope curves after TG12 at5.5 Ma (Fig. 6), interpreted to result in muchwarmer and humid globalclimates (Hodell et al., 2001; Hilgen et al., 2007). This resulted in apositive hydrological change and caused widespread transgression ofLago-Mare/Upper Evaporite facies over theMessinian erosional surfaces(Lofi et al., 2005; Roveri et al., 2008). Transgressional sequences areespecially clear in Northern Italy where they are attributed to anincreased hydrological flux from the Alps (Willet et al., 2006). The time-equivalent transgression in the Paratethys can also be explained bythese regional climatic changes.

The alternative hypothesis for this transgression is the re-establish-ment of Paratethys–Mediterranean connectivity by the Zanclean delugeof theMediterranean at theMiocene Pliocene boundary (5.33 Ma). Thiswould better explain the sharp transition from littoral and fluvialPortaferrian facies to predominantly pelitic facies in the lowerBosphorian. The Bosphorian ostracod and mollusc fauna do not showevidence of significant freshening of the water conditions, althoughtheir strontium isotope ratios suggest isolation from theMediterranean(Vasiliev, 2006). Mio–Pliocene connectivity at high sea level has earlierbeen suggested by Clauzon et al. (2005), but these authors based it onthe nannofossil influxes in the Paratethys at the Pontian–Dacianboundary which are dated at 4.7 Ma and have thus no relation at allwith the Pliocene flooding.We realize that a correlation to the Zancleanflooding cannot be excluded on the basis of our data. However,were theParatethys transgression to be coeval with the Mediterranean flooding,substantial changes in sedimentation rate would be required, especiallyby a major (4×) increase in the lowermost part of the Bosphorian(below the Thvera).We have not seen any evidence for such an increasein thefield, nor in the Râmnicu Sărat section (east Carpathian foredeep),nor in the Topolog region (south Carpathian foredeep). Future researchshould therefore aim at localizing marine influxes at the base of theBosphorian and focus on geochemical proxies that may quantifyParatethys–Mediterranean connectivity.

8. Conclusions

Our integrated stratigraphic data results in a robust chronologicalframework for the Dacian and Black Sea basins of the Eastern Paratethys(Table 1), allowing high-resolution stratigraphic correlations betweenthe individual Paratethys subbasins and with the Messinian SalinityCrisis of the Mediterranean (Fig. 6). The Maeotian/Pontian boundary isdated at 6.04 Ma and corresponds to amajor faunal change triggered by

a marine flooding of the Paratethys, as evidenced by the presence ofplanktonic foraminifera. The lowermost Pontian (Odessian/Novoros-sian) substage relates to a general high-stand in the Paratethys, possiblywith interbasinal and Mediterranean connections. The onset of MSCevaporites closely coincides in agewith the bloomofOdessian ostracodsin the Paratethys at ∼5.95 Ma. The peak of the MSC at 5.6–5.5 Madefinitely ended Mediterranean–Paratethys connectivity in the Porta-ferrian, causing a sudden drawdown of Paratethys water levels of atleast 50–100 m and isolating the Caspian Sea and the Dacian Basin fromthe Black Sea domain. From 5.5 Ma onward a major change in Eurasianclimate, resulting in much warmer and humid conditions changed thehydrological balance and resulted in a widespread transgression inMediterranean and Paratethys. The Miocene/Pliocene boundary maycorrespond to thePortaferrian/Bosphorianboundary in theDacianBasinand to the top of the red layer in Zheleznyi Rog, i.e. within the lowerKimmerian of the Black Sea Basin, but certainly not to the Pontian/Dacian boundary in the Dacian Basin, which is dated ∼600 kyr youngerat 4.7 Ma.

Our new stratigraphic framework has also serious consequences forthe Mediterranean MSC. Ever since the discovery of widespreadMessinian evaporites all over the Mediterranean seafloor, tectonic orglacio-eustatic processes restricting and closing the water exchange tothe Atlantic in the west have been put forward and modeled tounderstand the causes of the Messinian Salinity Crisis (Hsü et al., 1973;Meijer and Krijgsman, 2005; Ryan, 2009), but conclusive answers arestill lacking. Our data suggest that changing the connectivity to theParatethys in the northeast could play an essential role in the onset ofgypsum formation, which should give ample ammunition for new ideasand models concerning evaporite formation in semi-isolated basins.This will also havemajor implications for paleoceanographic circulationpatterns, Mediterranean paleosalinity models and the internal stratifi-cation of its water column.

Acknowledgements

WethankDan Jipa, Iulia Lazăr ar andGheorghePopescu for theirhelpwith sedimentological and biostratigraphical analyses of the RâmnicuSărat data. Alexandr Iosifidi is acknowledged for skilful paleomagneticsampling at Zheleznyi Rog. Cor Langereis, Frits Hilgen, Paul Meijer andPasha Karami are thanked for discussions and useful comments on anearlier version of this manuscript. Rachel Flecker, Miguel Garcés andfour anonymous EPSL reviewers are thanked for their constructivecomments. Sergei Yudin and Vika Tomsha assisted with the paleomag-netic analyses. This studywas performed under the inspiring leadershipof Cor Langereis and Alexei Khramov, within the NWO program onDutch–Russian cooperation. This workwas financially supported by theNetherlands Research Centre for Integrated Solid Earth Sciences (ISES)and the Netherlands Geosciences Foundation (ALW)with support fromthe Netherlands Organization for Scientific Research (NWO).

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