1IntroductionTheEocene-Oligocene(E-O)transitionwasanepochofgreatturnover,inbothterrestrialandmarineenvironments.MammalswerehighlyaffectedbyanextinctioneventcalledgrandecoupureofStehlin,which

hasbeenverywelldocumentedinEuropeandAsia(Hartenberger,1998).InAmericathetropicalmolluscsunderwentasignificantextinctioneventatthebeginningoftheOi-1glaciationintheOligocene(Hickman,

2003).ThisdropintemperaturewascausedbytheopeningoftheDrakeStrait,therebygivingrisetothecircumAntarcticcurrent,theformationoficecapsonthepolesandthedevelopmentofthepsychrospherein

thedeepocean(ShackletonandKennett,1975;KennettandShackleton,1976;BarkerandThomas,2004;Livermoreetal.,2005).EvidenceandcausesoftheEocene/Oligoceneevent,basedonextinctionandsurvival

patternsofforaminifera,werereviewedbyMolina(2015,seeotherreferencesherein).

Inorder toestablish theprecisechronologyof the turnoverat theE-O transition,as thePriabonianandRupelianstagestratotypesdurationwas imprecise, the InternationalCommissiononStratigraphy

organized a working group in 1980 to define the Eocene/Oligocene (E/O) boundary, which officially corresponded to the base of the Rupelian Stage. This task was undertaken by the International Geological

Plankticforaminiferalbiostratigraphy,paleoecologyandchronostratigraphyacrosstheEocene/OligoceneboundaryinnorthernTunisia

NarjessKaroui-Yaakoub a,b

ChaimaGriraa,b

MoncefSaïdMtimeta

MohamedHédiNegrab

EustoquioMolinac,∗

emolina@unizar.es

aDépartementdesSciencesdelaTerre,FacultédesSciencesdeBizerte,UniversitédeCarthage,Jarzouna,Bizerte,7021,Tunisia

bUnitédeRecherche:PétrologieSédimentaireetCristalline,UniversitédeTunisElManar,Tunisia

cDepartamentodeCienciasdelaTierra&IUCA,UniversidaddeZaragoza,E-50009,Zaragoza,Spain

∗Correspondingauthor.

Abstract

Thebiostratigraphicanalysis of theEocene-Oligocene transitionof theMenzelBouZelfa and Jhaff sections innortheasternTunisia (CapBonpeninsula) allowsus to identify a continuousplanktic

foraminiferalbiozonation.Thefollowingbiozoneswererecognized:GlobigerinathekasemiinvolutaZone(E14),GlobigerinathekaindexZone(E15),(HantkeninaalabamensisZone(E16)oftheupperEoceneand

Pseudohastigerina naguewichiensis Zone (O1) of the lower Oligocene. A rapidmass extinction event in planktic foraminifera occurred at the Eocene-Oligocene transition, including the extinction of the

turborotalids (Turborotalia cerroazulensis, Turborotalia cocoaensis and Turborotalia cunialensis) followed by a significant size reduction of the genus Pseudohastigerina and the extinction of the hantkeninids

(Hantkeninaalabamensis,Hantkeninabrevispina,HantkeninananggulanensisandCribrohantkeninalazzarii),whichmarktheEocene/Oligoceneboundary.Thesespeciesweretropicalandsubtropicalsurfaceand

intermediatedwellers,withdistinctivemorphologies(carinateturborotalidsandspinosehantkeninids),whichwerewelladaptedspeciesofk-strategy.Thesurvivingplankticforaminiferaspecieswerequite

similarinmorphologywithglobularchambers(globigerinids)andsmallplanispiral(pseudohastigerinids),whichwereopportunisticspeciesofr-strategy.Therecognitionofa4mthickinterval,betweenthe

extinctionofturborotalidsandhantkeninids,indicatesthatthesectioniscontinuousandoneofthemostexpandedthroughouttheEocene-Oligocenetransition.Thissectioncouldserveasanauxiliarysection

(hypostratotype)forthecompletedefinitionoftheGlobalStratotypeSectionandPointfortheEocene/Oligoceneboundary,whichmarkthebaseoftheRupelianStage.

Keywords:Plankticforaminifera;Eocene/Oligocene;Biostratigraphy;Paleoecology;Chronostratigraphy;Tunisia

CorrelationProgramme,Project174 ledbyCharlesPomeroland IsabellaPremoliSilva (PremoliSilvaand Jenkins,1993).Theworkinggroupsearchedworldwide for suitable sections,mainly inSpainand Italy.

Severalsectionswerevisited,sampledandstudiedintheBeticCordillera,southernSpainandtheproposedcandidatesweretheFuenteCalderasection(Molina,1980,1986;Comasetal.,1985),theTorreCardela

section (Martínez-Gallego andMolina, 1975) and theMolino deCobo section (Molina et al., 1988). These three sections showed an expanded stratigraphic interval based on planktic foraminifera, between the

extinctionoftheturborotalidsandthehantkeninids,spanningabout1minthickness,neverpreviouslyfoundinothersections,butalsofoundintheMassignanosectioninItaly(Molinaetal.,1986,1993;Nocchiet

al.,1988;GonzalvoandMolina,1992).IntheMassignanosectionthiscriticalstratigraphicintervalwaslessexpanded,butwhenthesectionwasmultidisciplinarystudied(PremoliSilvaetal.,1988),otherinteresting

datawere found.Consequently, theGlobalStratotypeSectionandPoint (GSSP) for thebaseof theOligocene (Rupelian)wasdefinedatmeter19of theMassignanosection,coincidingwith theextinctionof the

hantkeninids(PremoliSilvaandJenkins,1993).

SincethentheE/OboundaryhasbeenrecognizedworldwideandthebiostratigraphyoftheE-Ointervalhasbeenimproved.ArevisedgeochronologyandchronostratigraphywasproposedbyBerggrenetal.

(1995)andarevisedtropicalandsubtropicalPaleogeneplankticforaminiferalzonationwasproposedbyBerggrenandPearson(2005),Pearsonetal.Eds.(2006)andWadeetal.(2011).TheupperPaleogenedeposits

attractedtheinterestofsomeresearchersinTunisia,whowereabletofindtheEoceneandlowermostOligoceneinnortheasternandcentralTunisia(BenIsmail-Lattrache,1981,2000;Boukhalfaetal.,2009;Amami

Hamdi,2014;BenIsmail-Lattracheetal.,2014),inJordan(Farouketal.,2013,2015)andinEgypt(Orabietal.,2015).However,theywereneverabletofindthecriticalexpandedintervaloftheE/Oboundary.

TheaimofthisstudywastosearchforanexpandedcontinuousmarinesectioncrossingtheE/OboundaryinnorthernTunisia.AcompositesectionhasbeenfoundintheCapBonpeninsula:MenzelBouZelfa

andJhaffsections.Theplankticforaminiferalbiostratigraphyindicatesthatthiscompositesectionincludesaveryexpandedcriticalintervalbetweentheextinctionoftheturborotalidsandhantkeninids.Consequently,

thissectionissuitableandcouldbeapotentialauxiliarysection(hypostratotype)tocomplementthedefinitionoftheE/OboundarythatwasdefinedintheMassignanosection,Italy.

2Materialandmethods2.1Geologicalandgeographicallocation

TheMenzelBouZelfasectionislocatedintheCapBonpeninsula,north-easternTunisia,36°43'30.22″Nand10°42'15.57″E.ThesectionwassampledintheNEflankoftheJebelAbderrahmananticlinethatrisesto602min

height.Thestratigraphicseriesisessentiallycomposedofmarls,limestonesandsandsranginginagefromthemiddleEocenetoQuaternary(Fig.1).TheE/Oboundaryinthissectionwascoveredbyvegetationandsoil,preventinga

detailedsampling.However,thisintervalappearsverywellexposedattheJhaffsectioninthesameareaabout1kmsouthward,whichislocatedbetweenthecoordinatepoints36°42'16.44″Nand10°41'42.58″E.Atthiscriticalinterval

thesamples,whicharenamedJ6toJ13,arelocatedbycorrelationbetweensamplesMBZ26andMBZ25.

2.2MethodsInthefield,afirstloosesamplingwascarriedouttoidentifythelocationoftheboundaries.LateraregularsamplingatmeterintervalintheMenzelBouZelfasectionwascarriedout,andamoredetailedsamplingwastaken

acrossthecriticalintervaloftheE/OboundaryoftheJhaffsection.Inthelaboratory,samplesweresoakedintapwaterfortwodaysandH2O2wasaddedtosomeverycompactedsamples.Allsampleswerethenwashedthrougha

columnofsieves:250μm,100μmand63μm.ThewashedresidueswerecollectedintoPetridishesandstovedriedjustbelow50°C.Toperformthestatisticalanalysis,theresidueobtainedwassubdividedusingastandardmicro-

splitterOttotypetoobtainarandomnon-selectiverepresentativesample.Theselectedfractioncontainedatleast300individualsofplankticforaminifera,whichcanbeconsideredrepresentativeofthewholesample(Table1).The

dataobtainedweresubsequentlytreatedtodeterminethefrequencies(relativeabundance)ofrecognizedspeciesandtotracktheverticaldistributionofthesefrequenciesthroughoutthestudiedsection.Theresiduesweresorted

underabinocularmicroscopetoidentifytheplankticforaminiferaspeciesandtherestofthesamplewasscannedtolookforrarespecies.

Table1Tableofthequantitativeanalysisofplankticforaminiferaspecies.

alt-text:Table1

Samples Species

Catapsydraxdissimilis

Catapsydraxglobiformis

Catapsydraxhowei

Catapsydraxafricanus

Catapsydraxunicavus

Cribrohantkeninalazzari

Cribrohantkeninainflata

Dentoglobigerinatripartita

Dentoglobigerinagalavisi

D.pseudo-venezuelana

Globigerinathekasemiinvoluta

Globigerinathekaindex

MBZ1 0 0 0 0 0 0 0 0 0 0 0 0

MBZ2 0 0 0 0 0 0 0 0 0 0 0 0

MBZ3 0 0 0 0 0 0 0 0 0 0 0 0

MBZ4 0 0 0 0 0 0 0 0 0 0 0 0

MBZ5 0 0 0 0 0 0 0 0 0 0 0 0

Fig.1GeographicalandgeologicallocationoftheMenzelBoyZelfaandJhaffsections.

alt-text:Fig.1

MBZ6 0 0 0 0 0 0 0 0 0 0 0 0

MBZ7 0 0 0 0 0 0 0 0 0 0 0 0

MBZ8 0 0 0 0 0 0 0 0 0 0 0 0

MBZ9 0 0 0 0 0 0 0 0 0 0 0 0

MBZ10 0 0 0 0 0 0 0 0 0 0 0 0

MBZ11 X 0 0 0 0,19 0 0 0,38 2,2 1,7 0 0

MBZ12 X 0 0 0 0,2 0 0 0,4 0 3,5 0 0

MBZ13 0 0 0 0 X 0 0 0,3 0 2,6 0 0

MBZ14 X 0 0 0 0,3 0 0 0 5,5 7,9 0 0

MBZ15 X 0 0 0 X 0 0 0,6 0 1,5 0 0

MBZ16 0 0 0 0 X 0 0 7,2 2,4 1,9 0 0

MBZ17 X 0 0 0 X 0 0 0 1,1 2,5 0 0

MBZ18 X 0 0 0 0 0 0 1,3 0 7,4 0 0

MBZ19 X 0 0 0 0 0 0 0,7 0,5 1,1 0 0

MBZ21 X 0 0 0 0 0 0 0 0 0 0 0

MBZ22 0 0 0 0 0 0 0 0 0,3 0 0 0

MBZ23 0.31 0 0 0 0 0 0 0 0 0 0 0

MBZ24 0 0 0 0 0 0 0 0 0 0 0 0

MBZ25 X 0 0 0 0 0 0 0,3 0 0 0 0

Jhaff13 0 0 0 0 0,1 0 0 0,18 0,5 0 0 0

Jhaff12 0.19 0 0 0 0,06 0 0 0,19 1,2 0,6 0 0

Jhaff10 0 0 0 0 0 0 0 0 0,5 0 0 0

Jhaff9 0 0 0 0 0 0 0 0 0,6 0 0 0

Jhaff8 0 0 0,05 0 0,05 0,05 0 0,21 0,5 0 0 0

Jhaff7 0 0 0,1 0 0 0,05 0 0,26 1,4 0,9 0 0

Jhaff6 0 0 0 0 0,36 X 0 0 0,5 0,3 0 0

MBZ26 0 0 0 0 X 0 0,27 0,27 0 2,6 0 0

MBZ27 0 0 0,8 0 0 X X 0 0 2,5 0 0

MBZ28 0 0 0,3 0 X 0 0 0 0 0 0 0,8

MBZ29 0 0.15 0,3 0 0 0 0 0 0 0,9 0 0,1

MBZ30 0 0.32 0,32 0,3 0 0 X 2,9 4,5 5,8 1,6 1,9

Chilguembe-linaototara

Pseudohasti-gerinamicra

Ps.nague-wichiensis

Subbotinaeocaena

Subbotinacorpulenta

Subbotinajacksonensis

Subbotinaangiporoides

Subbotinalinaperta

Subbotinagortanii

Streptochilusmartini

Tenuitellainsolita

Tenuitellapraegemma

Turborotaliaincrebescens

Turborotaliaampliapertura

Turborotaliacocoaensis

MBZ1

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MBZ2

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MBZ3

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MBZ4

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MBZ5

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MBZ6

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MBZ7

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MBZ8

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MBZ9

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MBZ10

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

MBZ11

2,4 9,5 2,4 4,94 6,65 X 0,76 0 0 4,94 0 0,57 0,95 X 0

MBZ12

6,9 14,6 8,003 4,60 3,47 X 1,77 0 0 8,4 0 5,09 0,24 0,4 0

MBZ13

14,5 10,7 2,6 5,37 3,22 X 0 0 X 11,11 0 0,89 0,17 0,71 0

MBZ14

3,9 0,7 1,5 3,9 5,53 X 0,39 0 0 2,76 0 0 0 1,58 0

MBZ15

10,8 10,4 12,6 5,68 3,18 X 4,2 0 0 9,32 0 0,79 0,45 X 0

MBZ16

2,4 6,3 7,7 5,82 15,53 X X 0 X 1,94 0 1,94 4,36 4,36 0

MBZ17

3,3 5,3 8,3 8,65 7,26 X X X 0 2,51 0 3,91 1,95 1,11 0

MBZ18

10,2 6,4 7,8 1,36 3,4 X 0 X X 3,74 0 1,02 2,38 1,7 0

MBZ19

11,9 9,04 7,5 2,95 8,11 X X 0 0 9,04 0 0 1,6 3,5 0

19

MBZ21

18,4 9,7 7,1 5,88 5,62 0 0 X X 8,95 0 0 1,27 X 0

MBZ22

5,1 10,2 10,6 3,85 5,78 0 0 0 0 9,64 0 0 1,92 0 0

MBZ23

10,1 10,1 12,6 1,89 2,84 X X 0 0 6,01 0 1,58 0,94 0,63 0

MBZ24

21,7 8,1 15,9 1,55 1,94 X X X X 12,06 0 0 0 X 0

MBZ25

26,4 4 12 1,84 4,3 X X 0 0,61 15,08 0 0 1,23 X 0

Jhaff13

5,4 12,1 12,1 2 2,5 0 11,29 0 0,25 4,13 0 0 0,12 0,5 0

Jhaff12

5,3 9,08 9,6 4,54 4,28 0 7,39 0 0,38 4,41 0 0 0 1,94 0

Jhaff10

1,5 10,3 9,8 1,55 2,78 0 5,79 0 0,33 1,33 0 0 0,1 0,5 0

Jhaff9

5,1 9,6 12,5 3,59 4,35 0 5,38 0 0,26 2,55 0 0 0,2 0,53 0

Jhaff8

7,4 15,1 10,9 4,11 4,16 0 0,16 0 0,1 1,44 0 2,51 0,1 0,32 0

Jhaff7

4,4 7,07 7,02 4,2 6,92 0,62 0,57 0,2 0,15 1,35 0 0,52 0,5 0,57 0

Jhaff6

9,6 20,3 13,89 3,52 2,43 0,57 0 0,15 0,05 5,02 0 0 0,05 0 0,15

MBZ26

7,8 15,2 12,47 9,86 11,51 X 0 0,13 X 3,97 0 0 0 X 2,6

MBZ27

8,5 12,1 21,49 7,44 7,021 0 0 0 X 6,38 0 0 0,63 0 1,9

MBZ28

6,9 14,8 15,25 2,48 5,67 X X 0 0,35 17,38 1,41 0 0,17 0,17 0,35

MBZ29

7,8 13,8 13,66 5,31 5,46 X X 0 0,45 22,76 1,6 0 0,3 0,6 1,51

MBZ30

0 0,6 0 14,84 13,55 X 2,58 6,45 0,96 0 0 0 1,9 0 3,2

3Results3.1Lithostratigraphy

WesubdividedtheMBZsectionintothreelithostratigraphicunitsbasedonthefacieslithologicalvariations(Fig.2).UnitU1(MBZ30-Jhaff10)extendsover26mandcomprisedfriablemarls,lightgreyincolour,occasionally

interspersedwithcentimetricargillaceousreddishlimestonebedsandoxidesrichiniron.Themicropaleontologicalanalysisdeliveredawell-developedforaminiferalassociation,diversifiedandwellpreserved.Plankticforaminiferain

thisunitare representedbyspeciesbelonging to thegeneraSubbotina,Globigerinatheka,Globigerina,Turborotalia,Dentoglobigerina,Hantkenina,Cribrohantkenina,Catapsydrax, Pseudohastigerina, Tenuitella, Chiloguembelina,

Streptochilus, andGloborotaloides. In this unit, the Priabonian,which is largely developed in the Souar Formationwas identified. Ben Ismail-Lattrache (2000) recognized theGlobigerinatheka semiinvoluta and the Turborotalia

cerroazulensisBiozonesandconsideredthemasbelongingtothePriabonianstage .(seeFig.3)

Fig.2Compositestratigraphicaldistributionofplankticforaminiferalspecies.

alt-text:Fig.2

Fig.3Compositequantivativedistributionofplankticforaminiferalspecies.

UnitU2(MBZ25–Jhaff11)is20mthickandconsistsofmarlsdarkgreyincolourwithagreenishshade,interspersedatthetopbyacentimetriclevelofinduratedmarlwithferruginousconcretions.SampleJ11iscomposedof

asandylimestonebedrichinironoxides.Thissamplemarksatransitiontogreysandymarls.TheKorbousunit,whichreferstotheOligocene,overliesthelatePriabonianclays.ThiswasalsoreportedbyBenIsmail-Lattrache(2000),

whorecognized theCassigerinellachipolensis-Pseudohastigerinamicra,“Globigerina”ampliapertura,“Globorotalia”opima andGlobigerina ciperoensis biozones. This unit is poor in planktic foraminifera and shows a remarkable

reduction in the size of the taxabelonging to thePseudohastigerinagenus. The species foundbelong to thegeneraChiloguembelina, Pseudohastigerina, Streptochilus, Subbotina Turborotalia,Dentoglobigerina,Globorotaloides,

Tenuitella,Globoturborotalita,Catapsydrax,andGlobigerina.Furthermore,itischaracterizedbythepresenceofshark'steeth.Farouketal.(2015)recordedshark'steethandphosphateparticlesinJordansuggestingsomereworking.

UnitU3(MBZ10-MBZ1) is10mthickandbeginswithasandstonebedofabout2mthick,ochre inpatinaandyellow-to-beige inbreakageandrich inbioturbationtraces.Abovethisunit, lightgreymarlpredominates,

sometimesintercalatedwithsmallyellowish-to-brownishrustsmalllevelsrichinironoxides.Plankticandbenthicforaminiferaareveryrare,poorlypreservedanditwasextremelydifficulttoidentifythespecies,havingprobablybeen

reworked.Boukhalfaetal.(2009)foundasimilarunitonseveralsectionsinNorthernTunisia,composedofclayeysandstone,veryrichinPectenarcuatus, fossilplants, indicatingaveryshallowshelfenvironmentwithterrestrial

influence.Consequently,itsageisveryuncertainandislikelytobeupperRupelianorChattian.

3.2BiostratigraphyDuetotheirmarineenvironmentandtheirabundanceorfrequencyinplankticforaminifera,thestudiedmaterialhasallowedustorecognizethreebiozonescharacterizingtheupperEoceneandthelowermostzoneofthe

lowerOligocene(Fig.2).

TheGlobigerinathekasemiinvolutaBiozone,E14(Highestoccurrencezone)correspondstotheintervalbetweenthelastoccurrenceofMorozovelloidescrassatusandthelastoccurrenceoftheindextaxonGlobigerinatheka

semiinvoluta.ItcorrespondstothetopofthePorticulasphaerasemiinvolutaBiozone,P15ofBerggrenetal.(1995).ItisequivalenttotheGlobigerinathekasemiinvolutaBiozoneofBerggrenandPearson(2005)andWadeetal.(2011).

TheGlobigerinathekaindexBiozone,E15(Highestoccurrencezone)istheintervalbetweenthelastoccurrenceofGl.semiinvolutaandthelastoccurrenceofGlobigerinathekaindex,accordingtoBerggrenandPearson(2005)

andWadeetal.(2011),althoughthereisnointervalcorrespondingtoZoneP17.ItisalsoequivalenttotheupperpartoftheGl.semiinvolutaBiozoneandtothelowerpartofTurborotaliacunialensisandCribrohantkenina inflata

Biozone,P16ofBerggrenetal.(1995).

TheHantkeninaalabamensisBiozone,E16(Highestoccurrencezone)correspondstotheintervalrangebetweenthelastoccurrenceofGl.indexandthelastoccurrenceofH.alabamensis,accordingtoBerggrenandPearson

(2005)andWadeetal.(2011).AccordingtoBerggrenetal.(1995)itcoincideswiththeupperpartofTurborotaliacunialensisandCribrohantkeninainflataBiozone,P16andtotheT.cerroazulensisBiozone,P17.

ThePseudohastigerinanaguewichiensisBiozone,O1(Highestoccurrencezone)correspondstotheintervalrangezonebetweenthelastoccurrenceofH.alabamensisandthelastoccurrenceofPs.naguewichiensis,according

toBerggrenandPearson(2005)andWadeetal.(2011).ItcorrelatestotheTurborotaliacerroazulensis/Pseudohastigerinaspp.Biozone,P18,accordingtoBerggrenetal.(1995).

4Discussion4.1Biostratigraphy

Thebiostratigraphicalanalyseswerecarriedout inordertobetterknowarelevantplankticforaminiferaltimeintervalacrosstheEocene/Oligoceneboundary.Thestratigraphicdistributionsofthemostsignificantspecies

showninFig.2leadtotherecognitionoffourbiozonesandtheircorrelationtosimilarzonespreviouslyestablishedbyotherauthors.

Inthestudiedsectionwedidnotfindtherelevantextinctioneventofthelargemuricateplankticforaminifera,suchasAcarininaandMorozovelloides(Wade,2004),whichiswellrepresentedintheTorreCardelasection,Spain

(GonzalvoandMolina,1996),theAlanosection,Italy(Agninietal.,2011)andcharacterizestheBartonian-Priaboniantransition(Wadeetal.,2012a).ThelowermostpartoftheMenzelBouZelfasectioncorrespondstotheuppermost

partoftheE14biozone(middlePriabonian).

Thebasalpartofthesection,upto18m,canbeassignedtotheupperpartofthebiozoneE14definedbythelastoccurrenceofM.crassatusatthebaseandthelastappearanceofG.semiinvolutaatthetop(Berggrenand

Pearson(2005);Pearsonetal.,2006).ThisbiozoneisoverlainbythebiozoneE15,thetopofwhichismarkedbytheextinctionofG.indexBerggrenandPearson(2005);Molinaetal.,2006;WadeandPearson,2008;Wadeetal.,2011).

ThesetwobiozoneswerealsofoundinseveralsectionsinSpain(Martínez-GallegoandMolina,1975;Molina,1986;Molinaetal.,1986,1988,1993,2006),inItaly(Nocchietal.,1988;PremoliSilvaetal.,1988;GonzalvoandMolina,

1992)andinTanzania(WadeandPearson,2008;Pearsonetal.,2008).

alt-text:Fig.3

AmajorextinctioneventofplankticforaminiferaoccurredacrosstheE/Oboundary.Indeed,justbelowtheboundary,intheupperpartoftheBiozoneE16(sampleJ6)thereisasuddenextinctionofthreespeciesbelongingto

theTurborotaliagenus:T.cerroazulensis,T.cocoaensisandT.cunialensis.Theydisappear4mbelowtheEocene/Oligoceneboundary,whichismarkedbytheextinctionofhantkeninids,theeventusedtoofficiallydefinethisboundary

byPremoliSilvaandJenkins(1993).TheintervalbetweentheextinctionoftheturborotalidsandhantkeninidswasalsorecordedintheboundarystratotypesectioninMassignano,Italy(Nocchietal.,1988;PremoliSilvaetal.,1988;

GonzalvoandMolina,1992)spanningonly0.4m.TheextinctionpatternacrosstheE/Oboundarycanbeconsideredarapidmassextinctionevent(Molina,2015).

At the topof theE16 zone,we found theextinctionof the last speciesbelonging to theFamilyHantkeninidae:HantkeninaprimitivaandH.alabamensis (very rare in the uppermost part); the other species:Hantkenina

compressa,HantkeninananggulanensisandCribrohantkeninalazzariibecameextinctjustbelow.However,thehighestoccurrenceofCribrohantkeninainflata,characterizedbyveryinflatedglobularchambers,isquestionable,inour

sectionitbecameextinctjustabovetheextinctionofGlobigerinathekaindex,inthelowerpartofthezoneE16anddidnotreachtheE/Oboundary.Ontheotherhand,WadeandPearson(2008)andBerggrenandPearson(2005),did

notrecognizeC.lazzarii,withtherugosesquarechambers;theyconsidereditajuniorsynonymofC.inflataandindicatedasimultaneousextinctionofHantkeninaandCribrohantkeninainflata.

Furthermore,wenotethatotherspeciesbelongingtothePseudohastigerinagenusunderwentamajorturnover,thelargeronesbecomingextinctattheE/OboundaryandthesmalleronessurvivingintotheOligocene.Itis

remarkable that thegenusPseudohastigerinaapparentlyshowsdwarfingsynchronouswith theHantkeninidaeextinction (Milleretal.,2008;WadeandPearson,2008).P.naguewichiensis survived through the boundary and rare

specimensofP.micraarepresent intheOligocene,buttheyaresmallerthan150μmandareconsideredPseudohastigerinacf.micra.ThosebiostratigraphicdataareconsistentwiththeFuenteCalderasection insouthernSpain

(Molinaetal.,2006),theTanzaniasection(WadeandPearson,2008;PearsonandWade,2015)andtheNoroñasectioninCuba(Molinaetal.,2016).

On the other hand, we noticed that some species are found to survive above the E/O boundary, such as Subbotina gortanii, Subbotina angioporoides, Subbotina eocaena, Subbotina corpulenta, Catapsydrax unicavus,

Globoturborotalitaouachitaensis.Atthebaseof theOligocene, fiveotherspeciesrecordedarelativeabundance innumberof individuals.ThesespeciesareDentoglobigerinatripartita,Dentoglobigerinagalavisi,Dentoglobigerina

pseudovenezuelana,TurborotaliaampliaperturaandTurborotaliaincrebescens(Table1).

SubbotinajacksonensisandCatapsydraxhoweiareidentifiedconsistentlyduringthemiddletolateEocene.TheydisappearattheE/Oboundary,unliketosomeotherGlobigerinidae.AccordingtoBerggrenandPearson(2005),

CatapsydraxhoweiandSubbotinajacksonensisbecameextinctatthesametime,inthetopoftheE16biozone.However,inourstudywenoticedthatCatapsydraxhoweidisappearsjustbeforeSubbotinajacksonensis,whichcontinue

totheuppermostEoceneandbecameextinctatthesametimeastheHantkeninidae.

Furthermore,Molina(1980,1986,2015)notedthatintheBeticCordillerathespeciesCatapsydraxdissimiliswasneverfoundintheupperEoceneandappearsinthebaseoftheRupelianstage.However,thisspecieswas

foundbyBerggrenandPearson(2005)fromthelateEocene,continuedintheOligocene,andwasconsideredasurvivorspecies.InMBZandJhaffsections,weidentifiedthelowestoccurrenceofthisspeciesinthefirstbiozoneofthe

Oligocene,similartowhathappenedintheBeticCordillera,Spain.

4.2PaleoecologyInadditiontotheirutilityinbiostratigraphy,thesequenceofassemblagesoftheplankticforaminiferaprovidespaleoecologicaldataaboutthewatercolumnstructure(CoxallandPearson,2007;Pearsonetal.,2008;Alegretet

al.,2008).ThequantitativeanalysisoftheplankticforaminiferaintheMenzelBouZelfaandJhaffsections(Table1)showsthatthesepelagicformsarepresentandconstantlyabundantthroughoutthesectionexceptinafewturbiditic

levels( )(Fig.3). Indeed, just below theEocene/Oligoceneboundary, theplanktic foraminifera are representedmainlyby typical species of the intermediate surfacedwelling, suchas Turborotalia pomeroli, T. cocoaensis, T.

cunialensis,T.cerroazulensis,T.ampliapertura,Globigerinathekatropicalis,H.compressa,H.primitiva,H.alabamensis,Cr. inflata,Cr. lazzarii,Ps.naguewichiensis,Ps.micra,D.galavisi,S.eocaena,S.corpulenta,S. linaperta,S.

jacksonensis.Thisassemblageoftropicalspecies(suchasT.cocoaensisandT.cunialensis)andsubtropicalspecies(Ps.naguewichiensis)infactreflectsafavorableenvironmentforthedevelopmentofthesespecies,amongwhichthe

mostabundantareS.corpulenta,S.eocaena,Ps.micra(about10–15%),whichrequireintermediatedwelling(seePlate1).

Fig.4

Fig.4BiostratigraphiccorrelationacrosstheEocene/Oligoceneboundary.

alt-text:Fig.4

Plate1PhotographsA–C:GlobigerinathekasemiinvolutaKEIJZER.SampleMBZ30.ZoneE14.Scalebar=100μm.D–F:GlobigerinathekaindexFINLAY.SampleMBZ29.ZoneE15.Scalebar=100μm.G–I:Turborotaliacocoaensis(CUSHMAN).SampleMBZ27.

ZoneE16.Scalebar=50μm.J–L:Turborotaliacunialensis(TOUMARKINEETBOLLI).SampleMBZ26.ZoneE16.Scalebar=100μm.M,N:Cribrohantkeninainflata(HOWE).SampleMBZ27.ZoneE16.Scalebar=100μm.O–Q:Cribrohantkeninalazzarii

(PERICOLI).SampleJhaff8.ZoneE16.Scalebar=100μm.R–T:HantkeninaalabamensisCUSHMAN.SampleMBZ27.ZoneE16.Scalebar=100μm.U:StreptochilusmartiniPIJPERS.SampleMBZ27.ZoneE16.Scalebar=50μm.V:Pseudohastigerinamicra

(COLE).SampleMBZ12.ZoneO1.Scalebar=50μm.W:PseudohastigerinanaguewichiensisMYATLIUK.SampleMBZ12.ZoneO1.Scalebar=50μm.

ApproachingtheboundaryE/O,thepercentagesoftypicalsurfacedwellersdeclineandthischangewascharacterizedbytheextinctionofamajornumberofforaminiferaspecieswhichcharacterizesthetropicalclimate,such

asthespeciesofthegenusTurborotalia(T.cerroazulensis,T.cocoaensis)andtheHantkeninidaefamilyandthespeciesS.linaperta.ThesechangeswerealsoaccompaniedbyarelativedecreaseinthenumberofPs.naguewichiensisof

sizegreater than150μm, reflectinga significant change in theecologyof theenvironment inaccordancewith thecoolingof the sea surface (Wadeetal.,2012b). Furthermore, at theEocene/Oligoceneboundary, the curves of

frequencyshowaslightdecreaseinthefrequencyofmostformsexceptsomespeciessuchasCh.ototaraandSt.martini,whichareconsideredindicatorsofstress(Gebhardtetal.,2013).

Otherspecieswerefoundconsistentlythroughthesectionandsurviveddespitetheseclimatechanges,suchasT.ampliapertura,D.pseudovenezuelana,D.galavisi,D.tripartita,T. increbescens,C.unicavus,Ps.micra,Ps.

naguewichiensis,S.eocaena,S.corpulenta,withincreasingabundanceinallOligocenesamplesandareconsideredopportunisticspecies.Ontheotherhand,thebaseoftheOligoceneisasuitableenvironmentfortheseopportunistic

speciesthatshowedaslightdecreaseinpercentagejustbelowtheE/Oboundary.Theconsiderableincreaseintheirfrequencyreflectsadropinthetemperatureofthesurfacewaterandthereforeanexpansionoftheglobalvolumeof

iceculminatingintheOi-1glaciation.TheglobalclimatedecreaseintemperatureduringtheupperEocenewastriggeredbytheopeningoftheDrakeStrait,theisolationofAntarctica,thealbedoeffect,theformationofthecircum

Antarcticcurrentandthepsychrosphere(ShackletonandKennett,1975;KennettandShackleton,1976;Kennett,1977;BarkerandThomas,2004;Livermoreetal.,2005).

4.3ChronostratigraphyTheE/OboundarywasformallydefinedbytheRupelianGSSPatmeter19oftheMassignanosectioninItaly,coincidingpreciselywiththehantkeninidsextinction(PremoliSilvaandJenkins,1993).TheE/Oboundarywasdated

as33.9Ma(Vandenbergheetal.,2012).Thesedimentsof theMassignanosectionarepelagicmarinewithnoevidenceofanyhiatus,but theuppermostEocene ischaracterizedbya0.4m thick condensed interval between the

extinciónof the turborotalidsand thehantkeninids.Anothersection in Italy, theMonteCagnerosection,wasproposedasapotentialparastratotype for theMassignanoglobal stratotypesectionandpoint (GSSP)due to itsgood

integratedstratigraphicandastrochronologicalcalibrationoftheEocene-Oligocenetransition(Hylandetal.,2009),althoughtheintervalissimilarlycondensed.

TherecognitionofthisintervalintheTunisiansectionisaveryrelevantfindingbecauseitis4mthickandisoneofthemostexpandedknowntodate(Fig.4).OnlyinTanzaniaisthisintervalmoreexpanded,sinceitis5.2m

thickanditsdurationwasestimatedat65ky(Pearsonetal.,2008).IntheFuenteCaldera,TorreCardelaandMolinodeCobosectionsintheBeticCordillera,southernSpain,thisinterval is1.2mthickanditsdurationhasbeen

estimatedat40ky(Molina,2015).Nevertheless,inJordanFarouketal.(2013,2015)foundahiatusmissingthisinterval.

AuxiliarysectionsshouldbeproposedinordertoimprovethedefinitionoftheE/Oboundary.Theseauxiliarysections,alsoknownashypostratotypes,mustbeplacedindifferentregionstobettercorrelatetheE/Oboundary

worldwide.ThemostexpandedandcontinuoussectionsknownsofararelocatedinTanzania(drillingsite12),Spain(FuenteCalderasection)andTunisia(Jhaffsection),whichareverysuitableandshouldbeproposedasauxiliary

hypostratotypes.

5ConclusionsTheplankticforaminiferadetailedstudyoftheMBZandJhaffcompositesectionallowedustoestablishadetailedbiozonation.InthisTunisiansectionwewereabletorecognizethefollowingbiozones:the

upperpartoftheGlobigerinathekasemiinvolutaZone(E14),theGlobigerinathekaindexZone(E15),theHantkeninaalabamensisZone(E16)oftheupperEoceneandthePseudohastigerinanaguewichiensisZone(O1)ofthe

lowerOligocene.

WenoticedamajorturnovereventacrosstheEocene/Oligoceneboundary,thatwasmarkedbyanintervalbetweentheextinctionofturborotalidsandhantkeninids.Theextinctionpatterncanbeconsidereda

rapidmassextinctioneventsinceitlastedabout40–65ky.Therecognitionofthisintervalindicatesthatthesectionisverycontinuousandexpanded.AtthetopofthisintervalthereisdwarfingofthePseudohastigerina

genus,withonlythespecimensnolargerthan150μmsurvivingintotheOligocene.

Thespecies thatbecameextinctacross theE/Oboundaryweretropicalandsubtropicalsurfaceand intermediatedwellers,withdistinctivemorphologies (carinate turborotalidsandspinosehantkeninids),

whichwerewelladaptedspeciesofk-strategy.Thisextinctioneventwastriggeredbythecoolingthatculminated intheOi-1glaciation inthe lowermostOligocene.Thesurvivingplanktic foraminiferaOligocene

specieswerequitesimilarinmorphologywithglobularchambers(globigerinids)andsmallplanispiralpseudohastigerinids,whichweremainlyopportunisticspeciesofr-strategy.

TheTunisiansectionallowsustorecognizea4mthickintervalbetweenextinctionoftheturborotalidsandhantkenids,whichisoneofthemostexpandedknowntodate.OnlyinTanzaniaisthisintervalmore

expanded,sinceitis5.2m.InSpainthisintervalis1.2m.IntheE/OboundarystratotypedefinedinItalyitis0.4mthick.Asaresult,theTunisiansectioncouldbeaverysuitableauxiliaryhypostratotypetocorrelate

theE/Oboundaryworldwide.

alt-text:Plate1

AcknowledgementsWewouldliketothanktheresearchunitteam“Pétrologiesédimentaireetcrystalline”oftheFacultyofSciencesofTunis.ThisstudyreceivedfinancialsupportandassistancethroughProjectCGL2014-58794P

fromtheSpanishMinistryofScienceandTechnology(FEDERfunds)andtheConsolidatedGroupE05fromtheGovernmentofAragón.

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Highlights

• PlankticforaminiferaE14,E15,E16,O1ZonesareidentifiedacrosstheE/Oboundary.

• ThesectioniscorrelatedwithothersinTanzania,SpainandtheE/OGSSPinItaly.

• TurborotalidsandhantkeninidsunderwentarapidmassextinctionacrosstheE/O.

• TheextinctioneventattheE-Otransitionisrecordedinaveryexpandedinterval.

• TheTunisiansectionisaverysuitableauxiliarysectionfortheE/Oboundary.

Query:Yourarticleisregisteredasaregularitemandisbeingprocessedforinclusioninaregularissueofthejournal.IfthisisNOTcorrectandyourarticlebelongstoaSpecialIssue/Collectionpleasecontacts.murray@elsevier.comimmediatelypriortoreturningyourcorrections.Answer:Yes