Original article

Calcareous nannofossils and foraminifers herald the MessinianSalinity Crisis: The Pollenzo section (Alba, Cuneo; NW Italy)§

Les nannofossiles calcaires et les foraminifères annoncent la crise de salinité messinienne :la coupe de Pollenzo (Alba, Cuneo; NO Italie)

Francesca Lozar a,*, Donata Violanti a,b, Francesco Dela Pierre a,b, Elisa Bernardi a,Simona Cavagna a, Pierangelo Clari a, Andrea Irace b, Edoardo Martinetto a, Stefania Trenkwalder b

a Dipartimento di Scienze della Terra, Università di Torino, via Valperga Caluso 35, 10125 Torino, Italyb CNR Istituto di Geoscienze, sezione di Torino, via Valperga Caluso 35, 10125 Torino, Italy

Received 9 December 2008; accepted 20 July 2009

Available online 24 October 2009

Geobios 43 (2010) 21–32

Abstract

During the Messinian, the Mediterranean area experienced fast and prominent paleoenvironmental changes, culminating in the so-calledMessinian Salinity Crisis, with the deposition of the evaporitic series. This work investigates the micropaleontological assemblages in the pre-evaporitic sediments of the Sant’Agata Fossili Marls (SAF) of the Pollenzo section (Cuneo area, North Western Italy). A semiquantitative analysisis carried out on the upper part of the marly and pelitic sediments of the SAF underlying the first gypsum bed, ascribed to the Vena del Gesso Fm.(VDF). The studied interval belongs to the planktonic foraminifer Globorotalia conomiozea Zone and ‘‘non distinctive Zone’’ of Iaccarino and tothe calcareous nannofossil MNN11b/c Zone of Raffi et al. (1998, 2003) (Raffi et al., 1998; Raffi et al., 2003). Decrease of diversity and abundanceof the foraminifer and calcareous nannofossil assemblages is recorded 12 m below the VDG and clearly reflects environmental stress. From bottomto top, six paleoecological events are recorded: (1) the first peak abundance of ‘‘small’’ Reticulofenestra and the last recovery (LR) of planktonicforaminifers; (2) the peak abundance of Pontosphaera japonica and the last recovery of warm water taxa Discoaster spp.; (3) the last recovery ofbenthic foraminifers; (4) the co-occurring peak abundances of Helicosphaera carteri and Sphenolithus abies, and the last recovery of warm watertaxa Amaurolithus spp.; (5) the second peak of ‘‘small’’ Reticulofenestra; (6) the definitive disappearance of calcareous nannofossils. Thesepaleoecological events describe a progressive isolation of the basin from the world ocean and increasingly stressed environment (LR planktonicforaminifers; LR Discoaster spp.), increasing dysoxic to anoxic conditions at the sea floor (LR benthic foraminifers), shallowing of the watercolumn (peak of H. carteri), increasing salinity in surface waters (peak of S. abies), and enhanced nutrient concentration in surface waters (peak of‘‘small’’ Reticulofenestra); these are related to paleoenvironmental changes predating gypsum deposition at Pollenzo and affecting the wholeMediterranean basin.# 2009 Elsevier Masson SAS. All rights reserved.

Keywords: Calcareous nannofossils; Foraminifers; Messinian; Salinity crisis; Tertiary Piedmont basin

Résumé

Durant le Messinien, la région Méditerranéenne est le témoin de changements paléoenvironnementaux rapides et importants. Les assemblages ànannofossiles calcaires et foraminifères observés dans les sediments pré-évaporitiques des Marne de Sant’Agata Fossili de la coupe de Pollenzo(région de Cunéo, nord-ouest de l’Italie) et décrits dans ce travail, permettent de reconstituer les conditions paléoenvironnementales précédantl’épisode évaporitique. L’analyse semiquantitative a été réalisée sur la partie inférieure de la coupe, constituée d’une alternance de marnes et pélitesfeuilletées au dessous du premier niveau gypseux appartenant à la formation de la Vena del Gesso (VGF). L’intervalle étudié a un âge Messinieninferieur et est situé dans la Zone à foraminifère Globorotalia conomiozea de Iaccarino et dans la Zone à nannofossiles calcaires MNN11b/c deRaffi et al. (1998, 2003) (Raffi et al., 1998; Raffi et al., 2003). L’abondance relative et la diversité des associations à foraminifères et à nannofossiles

§ Corresponding editor: Fabienne Giraud.* Corresponding author.

E-mail address: francesca.lozar@unito.it (F. Lozar).

0016-6995/$ – see front matter # 2009 Elsevier Masson SAS. All rights reserved.doi:10.1016/j.geobios.2009.07.002

F. Lozar et al. / Geobios 43 (2010) 21–3222

calcaires diminuent 12 m sous le premier niveau gypseux. Dans l’intervalle étudié, six événements paléoécologiques sont reconnus : (1) un premierpic d’abondance de « petits » Reticulofenestra et la disparition des foraminifères planctoniques ; (2) un pic d’abondance de Pontosphaera japonica,contemporain de la dernière occurrence du genre d’eau chaude Discoaster spp. ; (3) la disparition des foraminifères benthiques ; (4) un picd’abondance simultané chez Helicosphaera carteri et Sphenolithus abies et la dernière occurrence du genre Amaurolithus spp. ; (5) un second picd’abondance de « petits » Reticulofenestra; (6) la disparition de tous les nannofossiles calcaires. Ces événements reflètent un isolement progressifdu bassin par rapport à l’océan ouvert entraînant un stress environnemental majeur (disparition des foraminifères planctoniques ; disparition desDiscoaster spp.), des conditions disoxiques à anoxiques sur le fond (disparition des foraminifères benthiques), une diminution de la tranche d’eau(pic de H. carteri) et une augmentation de la salinité en surface (pic de S. abies), puis des conditions eutrophes dans les eaux de surface (pic de« petits » Reticulofenestra).# 2009 Elsevier Masson SAS. Tous droits réservés.

Mots clés : Nannofossiles calcaires ; Foraminifères ; Messinien ; Crise de salinité ; Bassin tertiaire piémontais

1. Introduction

The Messinian stage is one of the most intriguing anddebated topics of the Neogene stratigraphy, because during thistime interval the Mediterranean region underwent drasticpaleogeographical, paleohydrological and paleobiologicalchanges, related to the so-called ‘‘Messinian salinity crisis’’(MSC; Hsü et al., 1973; Hsü, 1977; Clauzon et al., 1996;Krijgsman et al., 1999). In the last decades, the availability of aprecise time scale reconstructed on the basis of the integrationof different disciplines (biostratigraphy, cyclostratigraphy,magnetostratigraphy, physical stratigraphy) has allowed extre-mely detailed correlation among the different Messinian basinsof the Mediterranean area and has improved the knowledgeabout the different events responsible for the MSC and theirtiming (Rouchy and Caruso, 2006; Roveri et al., 2008). On thebasis of the model recently proposed by the CIESM (2008),three different stages may be distinguished within the MSC:

� d

uring the first MSC stage (between 5.96 and 5.6 Ma), hugeamounts of gypsum were deposited in shallow marginalbasins; in the deeper portions this interval is represented byeuxinic shales whose deposition started in early Messinian; � in the second stage (between 5.6 and 5.55 Ma), primary

(halite and K salts) and resedimented evaporites weredeposited in deep basins. The latter derived from thedismantling of the previously deposited evaporites;

� th e third stage (between 5.55 and 5.33 Ma) is characterized

by the deposition of primary sulphate evaporites (UpperEvaporites) and by freshwater/brackish terrigenous sedi-ments (‘‘Lago Mare’’).

The end of the MSC is marked by the deposition of Zancleanmarine sediments, whose base is dated at 5.33 Ma (CIESM,2008).

The stratigraphical and paleontological studies carried outby Carlo Sturani (1973, 1976) in the surroundings of Alba(Tertiary Piedmont Basin, North Western Italy) in the earlyseventies, gave fundamental contribution to the scientificdebate concerning the MSC. After the tragic death of Sturani,few paleontological studies, mainly devoted to the macrofossilassemblages (Cavallo and Gaudant, 1987; Gaudant andCavallo, 2008) or to the benthic/planktonic foraminifer

associations (Violanti, 1996; Violanti et al., 2007) have beencarried out on the Messinian succession of the TertiaryPiedmont Basin. Conversely, no data on the calcareousnannofossil (CN) assemblages have been published, even ifrecent studies (Wade and Bown, 2006; Manzi et al., 2007) havedemonstrated the potential of this group in unravelling thedramatic paleoceanographic events related to the onset of theMessinian salinity crisis.

In this paper we present the results of a micropaleonto-logic study carried out on the calcareous nannofossil andforaminifer assemblages preserved at the transition betweenthe pre-evaporitic and evaporitic sediments exposed in thePollenzo section located West of the town of Alba(Piedmont, Italy; Fig. 1). The results of this study allowto detail the paleoecological events heralding the MSC bothin the upper water column and at the sea floor and tohighlight the occurrence of discrete layers where oligotypicCN assemblages testify some major changes that affectedprimarily the upper water column prior to the MSC (Hsüet al., 1973; Hsü, 1977; Clauzon et al., 1996; Krijgsmanet al., 1999).

2. Regional geological setting

The Tertiary Piedmont Basin (TPB) is composed ofOligocene to Messinian sediments deposited unconformably,after the mesoalpine collisional event, on both alpinemetamorphic rocks and Apennine Ligurian units (e.g., Gelatiand Gnaccolini, 1988; Castellarin, 1994; Mutti et al., 1995;Roure et al., 1996). Deposition of these sediments was stronglyinfluenced by synsedimentary compressional tectonics, relatedto the building of the Apennine thrust belt. As a consequence,three main tectono-sedimentary domains deposited on differentcrustal blocks and characterized by different sedimentaryfeatures, developed during the Cenozoic (e.g., Biella et al.,1997): the Tertiary Piedmont Basin s.s. to the South, and theMonferrato and Torino Hill to the North, whose relationshipsare masked by Pliocene to Quaternary deposits (Fig. 1[a]). Thestudied section is located at the NW edge of the TPB s.s., in theLanghe domain. It is composed of continental to shallowmarine coarse-grained terrigenous sediments (Lower Oligo-cene) that are followed by a thick sequence (up to 4000 m) ofdeep-water facies that records a drastic increase of the

Fig. 1. (a) Structural scheme of the Tertiary Piedmont Basin (from Bigi et al., 1990, modified). Dotted area: Oligo-Miocene sediments; grey area: Messinian sediments;White area: Pliocene Quaternary deposits. TH: Torino Hill; MO: Monferrato; AM: Alto Monferrato; BG: Borbera Grue; PTF: Padanian Thrust Fronts; SVZ: SestriVoltaggio Zone; VVL: Villalvernia-Varzi Line. BM: location of the Bric della Muda section (Violanti et al., 2007). (b) Geographic location of the Pollenzo section (Star).

F. Lozar et al. / Geobios 43 (2010) 21–32 23

subsidence rate (Upper Oligocene-Tortonian; Gelati et al.,1993; Falletti et al., 1995).

The Messinian succession cropping out in this sector of theTPB begins with deep-water pre-evaporitic marine sediments(Sant’Agata Fossili marls, SAF) of early Messinian age (Sturaniand Sampò, 1973), followed by primary evaporites referred to asthe Vena del Gesso Formation (VGF; Clari et al., 2008). Thistransition, described as very sharp, would point to the suddendrop of the sea level heralding the MSC (Cita et al., 1978). The

VGF is composed of alternating gypsum beds and euxinic shales;according to Sturani (1973, 1976), it was deposited in a restrictedhypersaline lagoon. Further studies (Clari et al., 2008) haveallowed to subdivide the VGF into three members, each onecharacterized by a peculiar evaporitic facies:

� th

e lower member, composed of two or three beds of massiveand banded selenite, separated by dm-thick layers of euxinicshales;

F. Lozar et al. / Geobios 43 (2010) 21–3224

� th

FiLR

e middle member, composed of a 7 to 10 m-thick bed ofmicrocrystalline laminated gypsum (‘‘Gesso Balatino’’according to Sturani, 1973);

� th e upper member, consisting of euxinic shales and dm to

m-thick beds of laminated gypsum.

The VGF is unconformably overlain by continental andbrackish water terrigenous sediments (Cassano SpinolaConglomerates), correlatable to the ‘‘Lago Mare’’ depositsof the Mediterranean area. They are in turn abruptly followedby clayey deep marine sediments of Zanclean age (ArgilleAzzurre Fm.), related to the re-establishment of fully marineconditions following the MSC.

2.1. The Pollenzo section

The studied section is located on the left bank of the TanaroRiver, downstream with respect to the bridge leading to thevillage of Pollenzo (Fig. 1[b]). In the Pollenzo section, theupper part of the SAF, the entire VGF and the lower part of theCassano Spinola Conglomerates are excellently exposed.Only the upper part of the SAF (130 m thick), up to the lowerboundary of the VGF, has been sampled for this study. The

g. 2. Stratigraphic log of the Pollenzo section and distribution of selected calcareoBF: Last Recovery of benthic foraminifers; LR CN: Last Recovery of calcare

SAF consists of a cyclic alternation of cm-thick bioturbatedmarls and laminated euxinic shales. A 90 m-thick slumpedinterval, related to a regional scale deformation episode, isexposed in the section. In this interval, the bedding isintensively folded. Above the slump, the cyclic organizationof the sediments is still recognizable. It is evidenced by m-thick packages of strongly laminated euxinic shales,alternated to dm-thick beds of strongly cemented marls. Inthe pelitic beds, marine fishes (Lepidopus sp., Myctophumsp.), pteropods (Cavolinia sp.) and abundant wood andangiosperm leaves have been observed. In the top few metersof the SAF, we noticed an increase in organic debris andlaminated euxinic beds. A bed containing abundant remains ofthe euryhaline fish Aphanius crassicaudus has been found 3 mbelow the first selenitic gypsum bed. The upper boundary ofthe SAF is sharp and is marked by a dm-thick vuggy carbonatebed that is followed by primary evaporites possibly markingthe onset of the MSC. This event is interpreted as beingsynchronous all over the Mediterranean basin and occurring at5.96 Ma (Krijgsman et al., 1999). In the Pollenzo section, theprimary evaporites consist of 2 selenitic beds few meters thick(lower member of the VGF), a 7 m-thick bed of microcrystal-line laminated gypsum (middle member), followed by a pelitic

us nannofossil (CN) species. LR PF: Last Recovery of planktonic foraminifers;ous nannofossils. Percentages are relative to 500 counted specimens.

F. Lozar et al. / Geobios 43 (2010) 21–32 25

interval intercalated by several thin gypsum beds (uppermember) (Clari et al., 2008).

3. Materials and methods

The part of the section considered in this study belongsentirely to the SAF (Fig. 2); the lower part was sampled every1.5 m; the uppermost 2 m were sampled at 0.5 m interval; theslumped interval was only spot sampled (three samples). Atotal of 36 samples were studied for micropaleontologicalanalysis. CN assemblages were studied in smear slides at1250� under cross-polarized light microscope; slide prepara-tion was kept simple using standard techniques in order toretain the original composition of the sediments. Semi-quantitative analyses were carried out by counting at least 500specimens per slide (Appendix A). For very rare genera(Amaurolithus, Discoaster, Scyphosphaera, Thoracosphaera)frequencies were estimated by counting the number ofspecimens in 400 fields of view (FOV), corresponding to anarea of 9 mm2.

For foraminiferal and ostracod analyses, about 100–200 g ofdry sediment were gently boiled with water and sodiumcarbonate for 1–2 hours, then washed, dried and weighted into

Fig. 3. Stratigraphic log of the Pollenzo section and distribution of s

grain fractions > 250 mm, 250–125 mm and 125–63 mm. Foreach sample, the taxa distribution was investigated on the threeseparate fractions; semiquantitative analyses were performedon the total > 125 mm residue. The P/(P + B) ratio wasestimated on the average of the three separate fractions.

Taxa belonging to the genus Reticulofenestra were identifiedfollowing the taxonomic concept of Young (1998) and Wadeand Bown (2006). For specimens> 5 mm and with open centralarea, two size-ranges were distinguished: R. pseudoumbilicus(5–7 mm) and R. pseudoumbilicus large (> 7 mm). Theabundance frequencies of R. minuta (< 3 mm), R. haqi andR. antarctica (3–5 mm, with open and closed central area,respectively) are lumped together under the label ‘‘small’’Reticulofenestra, meaning all Reticulofenestra < 5 mm.

4. Results

In the lower part of the section, up to 25.5 m (Figs. 2 and 3),CN together with planktonic and benthic foraminifers werefrequent to abundant; mollusk, echinoid and fish fragmentswere common. Pteropod shells, generally pyritized, werelocally present. Ostracods were very rare. CN preservation wasmoderate to good. The thick slumped interval (�90 m) was spot

elected planktonic and benthic foraminifers. Legend as in Fig. 2.

F. Lozar et al. / Geobios 43 (2010) 21–3226

sampled in its upper part, but the three collected samples werebarren with respect to CN and foraminifers. Above this level,both foraminifer and CN assemblages showed an abruptdecrease in abundance and diversity; preservation of CNspecimens became poor.

Reworked CN of late Cretaceous, Oligocene and Mioceneage were also common to abundant from the base of the sectionup to 127 m (Fig. 2).

Finally, the absence of diatoms in all the samples isnoteworthy, since this group occurs quite often in coevalsediments of the region (e.g., Fourtanier et al., 1991; DelaPierre and Lozar, unpublished data) and in several sections ofthe Mediterranean region (e.g., Metochia, Frydas, 2006; Sicily,Blanc-Valleron et al., 2002; Cyprus, Wade and Bown, 2006).

4.1. Microfossil assemblages below the slump

From the base of the section up to 25.5 m (below the slump),CN assemblages were abundant and well preserved. They weredominated by open marine taxa, such as Reticulofenestra spp.,Coccolithus pelagicus, Calcidiscus leptoporus, Sphenolithusabies, and Helicosphaera carteri, together with less abundantwarm water taxa (Discoaster spp. and Amaurolithus spp.). Minorcomponent of the assemblage were Umbilicosphaera rotula,Pontosphaera spp., Scyphosphaera spp. and Thoracosphaeraspp. Species belonging to the genus Amaurolithus were very rarein the lower part of the section up to 15 m; above this level theyincrease in abundance up to 6/mm2 (Fig. 2); A. delicatus,A. primus and A. primus/delicatus intergrade are recorded fromthe base of the section. No specimen of Nicklithus amplificus wasrecovered in the studied material. Reticulofenestra rotaria wasrecovered from the very base of the section in very lowabundance. Directly below the slump, the assemblage isdominated by ‘‘small’’ Reticulofenestra (95% of the total).

In this interval (0–25.5 m), foraminifers were well to poorlypreserved; planktonic foraminifers were always dominant.Orbulina universa, Globigerina (Globoturborotalita) apertura,G. bulloides, G. obesa, G. extremus, G. obliquus, G. trilobusand Neogloboquadrina acostaensis are the most common taxa,and followed by G. suterae and Turborotalita quinqueloba. Inthe lowermost samples, rare specimens of G. conomiozea wererecognized (Fig. 3). G. nicolae was recorded from 7.5 m abovethe base up to 25.5 m. Benthic foraminifers, even ifquantitatively scarce, are well diversified within the lowermostresidues, up to about 10 m from the base of the section,and many outer neritic to bathyal species are common(Anomalinoides helicinus, Bolivina arta, Bulimina minima,Cibicidoides pseudoungerianus, Hoeglundina elegans, Karrer-iella bradyi, Lenticulina spp., Martinottiella communis,M. perparva, Melonis soldanii, Planulina ariminensis, Sig-moilopsis schlumbergeri, Uvigerina peregrina, U. striatissima).Deep bathyal taxa, such as Cibicidoides kullenbergi, Eggerellabradyi, Melonis pompilioides, Planulina wuellestorfi (VanMorkhoven et al., 1986), are rare. From 10 m above the baseupwards, the benthic diversity strongly decreased and most ofthe bathyal species disappeared (A. helicinus, C. kullenbergi,K. bradyi, M. pompilioides, U. peregrina, etc.). Stress tolerant,

infaunal taxa such as Bolivina spp., Bulimina spp. andGlobobulimina affinis as well as shallow water forms[Elphidium spp., Neoconorbina terquemi]; Murray, 2006)became common in the layer underlying the slump (25.5 m).

4.2. Microfossil assemblages above the slump

In the upper part of the section, above the slump, CNpreservation and abundance became low, but the assemblagescomposition was very similar to that of the lower samples;reworking of Cretaceous, Oligocene and Miocene taxa slightlyincreased with respect to the lower part of the section (0–

25.5 m; Fig. 2). Discrete layers with nearly oligotypic CNassemblages or where anomalous high abundances of rarespecies occurred, were recorded. The first one occurred at118 m, where the CN assemblage was dominated by ‘‘small’’Reticulofenestra (up to 98% of the total). At this level,foraminifer assemblages were very poor. Rare planktonicforaminifers, almost totally represented by T. quinqueloba,were found only in the layers immediately overlying the slump(118 m). No planktonic foraminifers were recovered in thesediments above this level. Benthic foraminifer taxa, repre-sented by rather common Bulimina echinata and Brizalina spp.(B. dilatata, B. spathulata), were recognized from 118 up to121 m (12 m below the first selenitic gypsum bed; Fig. 3).

At 119.5 m a sharp peak abundance (11% of the totalassemblage) of Pontosphaera japonica was recorded in CNassemblages; a minor coeval event is the unusual abundance ofScyphosphaera spp., a very rare taxon only seldom recorded inMediterranean sections. Discoaster spp., well-known warmoligotrophic water taxa (Gibbs et al., 2004; Bralower, 2002)were last recorded in this layer and disappeared above it.

At 121 m the last recovery of benthic foraminifer taxa wasrecorded.

At 122.5 m, CN assemblage was nearly oligotypic anddominated by S. abies and H. carteri (up to 60 and 20%,respectively). Amaurolithus spp., known to be warm oligo-trophic taxa, were last recorded in this layer and disappearedabove it. A minor paleoecological event was also recorded: theunusual abundance of Thoracosphaera spp., a very rare taxonof calcareous dinoflagellate only seldom recorded in Medi-terranean sections.

At 125.5 m, just 4.5 m below the first selenitic gypsum, thesecond peak abundance of ‘‘small’’ Reticulofenestra, up to 80%of the total assemblage, was recorded.

The final disappearance of CN was recorded at 127 m, 3 mbelow the first selenitic gypsum. Above 127 m the sedimentwas completely barren of CN, both as synsedimentary andreworked specimens.

5. Discussion

5.1. Biostratigraphy

The scattered but continuous occurrence of Amaurolithusspp. (A. primus, A. delicatus and A. primus/delicatusintergrade) and R. rotaria from the bottom of the section

F. Lozar et al. / Geobios 43 (2010) 21–32 27

allows the identification of CN zones MNN11b and MNN11c ofearly Messinian age, even if Nicklithus amplificus, the markerspecies of Zone MNN11c, does not occur in the studiedmaterial. The FO of this taxon is astrochronologically dated at6.689 Ma and marks the MNN11b/MNN11c boundary (Raffiet al., 2003). Despite its biostratigraphic use, mainly justified byextra-Mediterranean correlation purposes, N. amplificus wasrecently reported to be very rare (Cyprus, Morigi et al., 2007;Spain, Flores, pers. comm.) or absent (Manzi et al., 2007) inseveral Mediterranean sections, and therefore of little help forthe correct identification of MNN11c Zone lower boundary.

The presence of G. conomiozea from the bottom of thesection up to 25.5 m, below the slump, confirms the Messinianage of the section and allows the correlation to theG. conomiozea Zone of Iaccarino (1985). The first recoveryof G. nicolae was recorded at 7.5 m above the base. The FO ofthis taxon is dated at 6.83 Ma and its LO to 6.72 Ma by Lourenset al. (2004); this taxon has a very short range and disappears inthe Pollenzo section at 25.5 m, indicating an age not youngerthen 6.72 Ma for the sediments cropping out just below theslump (Fig. 3). Moreover, the recovery of G. nicolae in thelower part of the Pollenzo succession allows the correlationwith the coeval Bric della Muda laminites (see location map inFig. 1[a]; Violanti et al., 2007), where the taxon also occurred.

The occurrence of B. echinata, whose FO is dated to 6.29 Ma(Kouwenhoven et al., 2006) indicates an age of 6.29 Ma oryounger for the sediments overlaying the slump (Fig. 3).

5.2. Microfossil paleoecological events before the onset ofgypsum deposition

The P/(P + B) ratio of foraminifer assemblages (Fig. 3) wasestimated to give an approximate evaluation of palaeobathy-

Fig. 4. Stratigraphic log of the Pollenzo section and position of m

metry (Boltovskoy and Wright, 1976). In most of the lower partof the Pollenzo succession the P/(P + B) ratio ranged between80–90%, suggesting a deposition in the bathyal zone (Wright,1978). The plankton percentage decreased to about 70% justbelow the slump. In the part of the section below the slump, CNassemblages show sharp abundance fluctuations of selectedspecies, but sampling interval was too loose to infer a goodcorrelation with the recognized lithologic cycles.

Nevertheless, from 19 to 25 m, Discoaster spp. abundancesincreased from base to top of each laminated marls anddecreased from bottom to top of each homogeneous marls ofthe two lithologic cycles, possibly related to nutrient fluctuationin the photic zone. In the same interval, ‘‘small’’ Reticulofe-nestra showed an increased abundance from bottom to top.‘‘Small’’ Reticulofenestra has been reported as living ineutrophic, normal to mixed marine conditions (Flores et al.,2005) and as being abundant in shallow waters and near-shoreenvironments in the Messinian Paratethys (Golovina, 2008).‘‘Small’’ Reticulofenestra has also been recorded in highabundances in Tortonian/Messinian sections (e.g., Faneromeni,Crete) where it has been interpreted as indicative of highfertility surface waters (Negri and Villa, 2000). The ‘‘small’’Reticulofenestra high abundances here recorded could testifyincreased nutrient availability in surface waters and couldsuggest a slight shallowing of the water column in this timeinterval, as also testified by the decreasing P/(P + B) ratio. Atpresent, a more detailed analysis is in progress in order to testwhether these fluctuations could be related to climatic cycles.

Above the slump, the P/(P + B) ratio (Fig. 3) of theforaminifer assemblages showed a strong reduction to less than20% and documented the shallowing of the water column aswell as the progressively adverse condition of the water mass.The reduction of benthic foraminifer diversity and the loss of

ain microfossil paleoecological events. Legend as in Fig. 2.

F. Lozar et al. / Geobios 43 (2010) 21–3228

deep bathyal taxa widely preceded the P/(P + B) decrease andsuggest that the evolution from normal marine condition tobasin confinement strongly affected the sea bottom well beforethe surficial or intermediate water column, as documented inthe southern Mediterranean area (Kouwenhoven et al., 1999;Blanc-Valleron et al., 2002; Drinia et al., 2004) as well as in thePiedmont basin (Sturani and Sampò, 1973; Violanti et al.,2007).

Several major paleoecological events affecting the CNassemblages were recorded in the same stratigraphic interval(Fig. 4), also suggesting an increasingly stressed environmentin the upper water column and shallowing of the basin.

Recently, several hypotheses have been made on LateMiocene CN response to the onset of the MSC and on thepossibility of temporary marine connection at time of gypsumdeposition; the occurrence of oligotypic CN assemblages hasbeen noted in sediments below and interbedded to the massivegypsum by Wade and Bown (2006) and Kouwenhoven et al.(2006) among others. In the present study, we found sixpaleoecological events and we discuss their paleoceanographicmeaning, their usefulness in describing the onset of the MSC,and their potential for regional correlation at the Mediterraneanscale.

5.2.1. The first ‘‘small’’ Reticulofenestra peak and LastRecovery of planktonic foraminifers

The first ‘‘small’’ Reticulofenestra peak abundance is thefirst paleoecological event above the slump and occurs at118 m, together with the Last Recovery (LR) of planktonicforaminifers. ‘‘Small’’ Reticulofenestra has been reported asliving in eutrophic, normal to mixed marine conditions (Floreset al., 2005) and as being indicative of high fertility surfacewaters (Tortonian/Messinian section of Faneromeni, Crete;Negri and Villa, 2000). Moreover, it occurs in high abundancesin sediments deposited in shallow waters and near-shoreenvironments in the Paratethys during the Messinian (Golovina,2008). The high abundance recorded here would suggest atemporary enhancement of the nutrient supply in the upperwater column and/or neritic environment.

5.2.2. The anomalous peak abundance of Pontosphaera

japonica

The anomalous peak abundance of P. japonica is the secondpaleoecological event in the Pollenzo section and is recorded at119.5 m. This taxon has also been recorded in the Polemi Basin(Cyprus, Eastern Mediterranean) in the pelitic beds underlyingthe massive gypsum, testifying that P. japonica could thrive instressed environment (Wade and Bown, 2006), but is otherwisevery rare in tropical marine assemblages. Little is known aboutpaleoecological affinities of Pontosphaera despite the long life-range of this taxon, and this is the first time its anomalousabundance is recorded in Mediterranean Messinian sections.Chira and Igritan (2004) suggest that Pontosphaera is anearshore taxon and tolerates low salinity environments duringthe Eocene and Oligocene. The occurrence of anomalousabundance of P. japonica 10.5 m below the gypsum bed and1.5 m above the LR of planktonic foraminifers suggests that

this nearshore taxon could live in a stressed environment, andprobably tolerates both high and low salinity conditions; itcould thrive in the upper water column when it was alreadyexperiencing adverse life conditions for the calcareousplankton; at this time, the connection with the open oceanwas probably already interrupted or discontinuous. The stresstolerating character of P. japonica is further supported by itsoccurrence in the pelitic sediments intercalated to the massivegypsum beds in the Polemi Basin (Wade and Bown, 2006).

5.2.3. The disappearance of warm water taxa Discoaster

spp.The disappearance of warm water taxa Discoaster spp. in the

CN assemblage is another noteworthy paleoecological event;these taxa are usually rare but continuously occurring from thebottom of the section and sharply disappear at 119.5 m (9 mbelow the first gypsum bed). The disappearance of open marinewarm water meso- to oligotrophic taxa (Raffi et al., 1998)supports the hypothesis that restricted conditions increasedduring this time interval.

5.2.4. The last recovery of benthic foraminifersThe last recovery of benthic foraminifers (LR BF) at 121 m

furthermore supports the hypothesis of isolation of the basinfrom the world ocean, impeding bottom water ventilation andcausing anoxia at the sea floor. This event is preceded byincreasing eutrophic conditions and decrease of bottom oxygencontent testified by the common Bolivinids and G. affinis, taxaadapted to low oxygen content and abundant organic matter.

5.2.5. The peak abundances of Sphenolithus abies andHelicosphaera carteri

The peak abundances of S. abies and H. carteri is anothersharp paleoecological event recorded at 122.5 m. S. abies andH. carteri usually are minor component of the assemblage,which is dominated by Reticulofenestra spp., and account forup to 2–3% of the total assemblage in the whole section. Thisstriking high frequencies are interpreted as a pristine pattern ofthe assemblage, since reworking could not have concentratedsuch great number of specimens. Relatively good preservationexcludes moreover that such an anomalous concentration is dueto selective dissolution.

5.2.5.1. Sphenolithus abies. S. abies is an extinct taxonusually common in warm oligotrophic waters (Aubry, 1998;Bralower, 2002; Gibbs et al., 2004), associated with Discoasterspp. (Perch-Nielsen, 1985) and interpreted as a k-selectedspecies. Monospecific assemblages of S. abies have beenrecorded in the Polemi Basin (Cyprus) in diatom-richMessinian sediments interbedded to and underlying the massivegypsum, thus suggesting a high nutrient level in surface watersat time of deposition. On the one hand, such occurrences couldreflect a shift of this taxon toward more r-selected life strategieswhen facing stressed environments; one the other hand, thesepeaks have also been interpreted as testifying temporaryconnection with the open ocean and normal salinity conditionsjust before and during the MSC (Wade and Bown, 2006).

F. Lozar et al. / Geobios 43 (2010) 21–32 29

A similar peak abundance of S. abies has recently beenrecorded in other Mediterranean sections, where it occurs at thetop of MNN11c Zone (Djebel Ben Dourda section, Algeria,Mansouri et al., 2008; Pissouri section, Cyprus, Kouwenhovenet al., 2006; Fanantello core, Central Italy, Manzi et al., 2007).In Pissouri (Kouwenhoven et al., 2006) and Fanantello (Manziet al., 2007) sections, a peak abundance of 60% or more islocated in the precession-controlled sedimentary cycle justbelow the onset of the MSC. In both sections three peaks arerecorded, but in Pissouri all of them occur below the firstgypsum bed (between 6.3 and 5.98 Ma; Kouwenhoven et al.,2006), whereas in Fanantello, the first peak is just below the LRof planktonic foraminifers, that is correlated to the base of thefirst gypsum bed of the Vena del Gesso Formation (Manzi et al.,2007); the remaining two peaks (up to 20 and 10%,respectively) are correlated to the fifth and sixth evaporiticcycles of the VGF (Lugli et al., 2005; Manzi et al., 2007). Thisdatum supports the idea of temporary connections of theMediterranean with the open ocean during lower gypsumdeposition, as also recorded in the Polemi Basin (Wade andBown, 2006).

The peak abundance (up to 60%) of S. abies recorded in thePollenzo section and its stratigraphic position suggest that thisevent could be correlative of the peaks recorded at Pissouri andFanantello and slightly preceding the beginning of theevaporitic phase; abundances recorded both in the Pissouriand Fanantello sections are very similar and occur just belowthe LR of planktonic foraminifers, whereas in our section thispeak occurs 4.5 m above this datum. Since this part of thesection lacks very detailed age constraints, we are presentlyunable to clarify if the S. abies peak abundance recorded atPollenzo could be correlative of the first peak of Manzi et al.(2007), thus identifying the uppermost pre-evaporitic sedi-ments, or with the upper peaks, thus suggesting that in thePollenzo section a deep water counterpart of the LowerEvaporites is also recorded. Magnetostratigraphic and cyclos-tratigraphic analyses of the section are in progress, aimed tobetter constrain the age of this and others paleoecologicalevents thus supporting one of the two hypotheses.

The co-occurrence of S. abies peak abundance withabundant H. carteri (a taxon presently thriving in meso- toeutrophic waters, Ziveri et al., 2000), supports the hypothesisthat prior to and/or during the MSC (Wade and Bown, 2006;Manzi et al., 2007), S. abies, usually a warm oligotrophic watertaxon, could thrive also in restricted and stressed environmentswith high nutrient input and possibly high salinity, in basinsprobably experiencing short-lived connection with the openocean. Anomalous high abundance of S. abies suggests thatprior to and during the MSC its behaviour was not limited bynutrient level but was more likely controlled by unfavourablelife conditions for most of CN taxa, possibly due to high salinityin surface waters.

5.2.5.2. Helicosphaera carteri. H. carteri is an extant taxontolerating salinity fluctuations and thriving in meso- toeutrophic waters (Ziveri et al., 2000), both in neritic (Cachãoet al., 2002) and oceanic environments; its presence today in the

Black Sea may suggest that this taxon has a high salinitytolerance range (Bukry, 1974). From the fossil record H. carteriis reported in shallow, eutrophic environments, with higherabundances in near-continental upwelling regions (Perch-Nielsen, 1985; Giraudeau, 1992); in Mediterranean Messiniansections it occurs with high abundances and its presence iscorrelated to eutrophic surface waters and fluctuating or highsalinity (Negri and Villa, 2000; Kouwenhoven et al., 2006;Flores et al., 2005).

In the Pollenzo section the coeval relatively high abundancesof H. carteri and S. abies suggests that S. abies abundance couldbe here mainly driven by salinity fluctuation, whereas the peakof H. carteri suggests an increasingly shallow water columnwith enhanced nutrient availability in surface waters.

5.2.6. Last Recovery of Amaurolithus spp.At this level another paleoecological event occur, the last

recovery of Amaurolithus spp., usually rare but continuouslyrecovered from the bottom of the section; they sharplydisappear at 122.5 m, supporting the idea of restrictedconditions in the basin.

5.2.7. The second ‘‘small’’ Reticulofenestra peakThe second peak of ‘‘Small’’ Reticulofenestra is the fifth

paleoecological event; at 125.5 m the assemblage is almostoligotypic and dominated by this taxon, reaching up to 90% ofthe total. In agreement to previous findings in otherMediterranean sections (Faneromeni, Negri and Villa, 2000),this event suggests high nutrient availability in the upper watercolumn, and a possible temporary connection to the open oceanat time when the Mediterranean water column was alreadyexperiencing increasing salinity and stratification; this isfurthermore supported by the occurrence of gypsum crystalsdispersed in the sediment. We agree with Morigi et al. (2007)that the peak abundance of ‘‘small’’ Reticulofenestra is a verysharp paleoecological event recorded in the Mediterranean, andis possibly very useful for regional scale correlations. Never-theless, this event needs to be studied in coeval sections of thearea, since its meaning is so far not completely understood.

5.2.8. Last Recovery of Calcareous NannofossilsIn the Pollenzo section the final disappearance of CN is the

last paleoecological event and it occurs at 127 m. Due to theabsence in the sediments above this level of both synsedimentaryand reworked CN, it is not clear whether the upper water columnwas, by this time, totally unsuitable for their life and theterrigenous input from the surrounding land slowed or stopped,or if subsequent diagenetic processes hindered their preservation.

5.2.9. Additional minor microfossil eventsTwo additional minor events are recorded respectively at

119.5 and 122.5 m, the unusual presence of Scyphosphaera spp.and Thoracosphaera spp., taxa that are virtually absent alongthe entire section. Very little is known about their ecology andpaleoecology. Scyphosphaera spp. is very rare in oceanicsediments and it occurs mainly in neritic and low latitudesedimentary environment (Perch-Nielsen, 1985). It could be

F. Lozar et al. / Geobios 43 (2010) 21–3230

tentatively associated here with shallowing of the watercolumn, as also supported by the high abundance ofP. japonica. Thoracosphaera spp. is a rare extant calcareousdinoflagellate genus that thrives in the lower photic zone, inrelatively lower temperature and higher salinity waters withrespect to normal marine conditions of the upper photic zone(Karwath et al., 2000); it is also reported in the fossil record aseutrophic, tolerating unstable and stressed environments(Pissouri section, Kouwenhoven et al., 2006). Its co-occurrencewith peak abundances of S. abies and H. carteri shows that thistaxon thrived in meso- to eutrophic waters with high orfluctuating salinity.

The absence of pentaliths such as Braarudosphaerabigelowi, well adapted to near-shore environment possiblysimilar to those developed in the TPB in this time interval, alsosuggests a fluctuating salinity in the upper water column, sincethis taxon is mainly recorded in near-shore low salinityenvironments in present-day and fossil records (Black Sea,Bukry, 1974). The high frequencies of taxa such as H. carteriand ‘‘small’’ Reticulofenestra also suggest a neritic environ-ment, but do not allow to better constrain paleo-water depth.Nevertheless, a shallower water column with respect to thelower part of the section could also be envisaged on the basis ofincreasing occurrence in the upper 4.5 m of the SAF of thinsandy layers, increasing plant debris (palm leafs) and fishremains (Aphanius crassicaudus).

The occurrence of disoxic and stress tolerating taxa amongthe benthic assemblages (B. echinata, B. dilatata) documentsthat bottom water oxygen depletion, surface eutrophication andwater column stratification occurred during the deposition ofthe upper part of the SAF, well before the actual onset ofgypsum deposition (130 m). Finally, the occurrence of well-preserved Aphanius crassicaudus (an euryhaline fish) at125.5 m also confirms that, by this time, the water columnalready experienced high salinity.

6. Conclusions

The Sant’Agata Fossili Marls cropping out in the Pollenzosection are of early Messinian age as demonstrated by therecovery of markers of the MNN11b/c Zone and of theG. conomiozea Zone. The sediments above the slump are notolder then of 6.29 Ma, as suggested by the occurrence of thebenthic foraminifer B. echinata. Both CN and foraminiferassemblages demonstrate that gypsum deposition at Pollenzowas preceded by a progressive deterioration of the normallymarine conditions with increasing stratification, increasingsurface salinity and shallowing of the water column, as alreadyhypothesized in different Mediterranean sections (Cyprus,Kouwenhoven et al., 2006; Wade and Bown, 2006; Sicily,Gautier et al., 1994; Bellanca et al., 2001, among others).Moreover, increasing bottom water anoxia and high nutrientavailability are suggested by the common to frequent benthicforaminifer taxa that tolerate low oxygen content and abundantorganic matter at the sea floor (Bolivinids and G. affinis).

Among the CN assemblages, six paleoecological eventsherald the MSC and are recorded in the upper 12 m of the

section, below the first gypsum bed. They are, from bottom totop:

� d

isappearance of planktonic foraminifers and peak abun-dance of ‘‘small’’ Reticulofenestra, indicating adverse lifecondition in the upper water column and increased nutrientavailability, respectively; � p eak abundances of P. japonica and Scyphosphaera spp.,

testifying continuously increasing salinity and shallowing ofthe water column, co-occurring with the disappearance ofwarm water oligotrophic taxa (Discoaster spp.), suggestingincreased separation of the basin from the world ocean andpossibly increased nutrient availability;

� d isappearance of benthic foraminifers, suggesting bottom

water anoxia, probably related to increased stratification ofthe water column, increasing nutrient supply in the upperwater column and increased separation of the basin from theworld ocean;

� p eak abundances of S. abies and H. carteri, supporting a further

increase in surface water salinity and shallowing of the watercolumn; the unusual occurrence of Thoracosphaera spp. alsosuggests high nutrient availability in the upper water column;

� th e last peak of ‘‘small’’ Reticulofenestra, demonstrating a

high nutrient input, probably related to further shallowing ofthe water column and proximity to the coastal area;

� th e last recovery of CN, possibly due to a further

enhancement of the environmental stress.

These data confirm that the disruption of normally marineconditions started before the beginning of precipitation of theselenitic gypsum. Moreover, shallowing of the water columnduring this time interval is supported by the occurrence ofneritic taxa in the CN assemblage, by the reduction of the P/(P + B) ratio to less than 20%, and by the increased plant debrisand increased occurrence of arenitic layers. Further studies(magnetostratigraphy, cyclostratigraphy) are needed to deci-pher the exact time frame of this sedimentary section, in orderto unravel its correct correlation to the pre-evaporitic and/orevaporitic sediments of the Messinian salinity crisis and toclarify the timing of gypsum deposition at this far end of theLate Miocene Adriatic gulf.

Acknowledgements

This study received financial support by MIUR funding (ex60%) to D. Violanti and P. Clari and by CNR IGG Torino,Commessa TA PO1-006. Giuliana Villa, Fabienne Giraud andan anonymous reviewer are acknowledged for their revisionsand comments that greatly improved this paper.

Appendix A. Taxonomic list of the calcareousnannofossils counted in the Pollenzo section.

Taxonomy in general follows that outlined in Perch-Nielsen(1985) and Young (1998).

� A

maurolithus delicatus Gartner and Bukry, 1975

F. Lozar et al. / Geobios 43 (2010) 21–32 31

� A

maurolithus primus (Bukry and Percival, 1971) Gartner andBukry, 1975 � C alcidiscus leptoporus (Murray and Blackman, 1898)

Loeblich and Tappan, 1978

� C alcidiscus macintyrei (Bukry and Bramlette, 1969) Loe-

blich and Tappan, 1978

� C alciosolenia murrayi Gran, 1912 � C occolithus pelagicus (Wallich, 1871), Schiller, 1930 � C oronocyclus nitescens (Kamptner, 1963), Bramlette and

Wilcoxon, 1967

� D iscoaster asymmetricus Gartner, 1969 � D iscoaster braarudi Bukry, 1971 � D iscoaster brouweri Tan, 1927 emend. Bramlette and Riedel,

1954

� D iscoaster challengeri Bramlette and Riedel, 1954 � D iscoaster deflandrei Bramlette and Riedel, 1954 � D iscoaster loeblichii Bukry, 1971 � D iscoaster pentaradiatus (Tan, 1927) Bramlette and Riedel,

1954

� D iscoaster quinqueramus Gartner, 1969 � D iscoaster variabilis Martini and Bramlette, 1963 � H elicosphaera carteri (Wallich, 1877) Kamptner, 1954 � L ithostromation perdurum Deflandre, 1942 � P ontosphaera discopora Schiller, 1925 � P ontosphaera japonica (Takayama, 1967) Nishida, 1971 � P ontosphaera multipora (Kamptner, 1948) Roth, 1970 � P ontosphaera syracusana Lohmann, 1902 � R eticulofenestra Hay, Mohler and Wade, 1966. These are

generally size-defined following the taxonomy outlined inYoung, 1998.

� R eticulofenestra antarctica (Haq, 1976) Driever, 1988 � R eticulofenestra haqii Backman, 1978 � R eticulofenestra minuta Roth, 1970 � R eticulofenestra pseudoumbilicus Gartner, 1967, 1969>7 mm � R eticulofenestra rotaria Theodoridis, 1984 � R habdosphaera clavigera Murray and Blackman, 1898 � R habdosphaera procera Martini, 1969 � S phenolithus abies Deflandre in Deflandre and Fert, 1954 � S cyphosphaera lagena Kamptner, 1955 � S cyphosphaera pulcherrima Deflandre, 1942 � S cyphosphaera globulata Bukry and Percival, 1971 � S yracosphaera pulchra Lohmann, 1902 � T horacosphaera Kamptner, 1927 � U mbilicosphaera jafari Müller, 1974 � U mbilicosphaera rotula (Kamptner, 1956) Varol, 1982.

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