15
1 Introduction The Eocene-Oligocene (E-O) transition was an epoch of great turnover, in both terrestrial and marine environments. Mammals were highly affected by an extinction event called grande coupure of Stehlin, which has been very well documented in Europe and Asia (Hartenberger, 1998). In America the tropical molluscs underwent a significant extinction event at the beginning of the Oi-1 glaciation in the Oligocene (Hickman, 2003). This drop in temperature was caused by the opening of the Drake Strait, thereby giving rise to the circum Antarctic current, the formation of ice caps on the poles and the development of the psychrosphere in the deep ocean (Shackleton and Kennett, 1975; Kennett and Shackleton, 1976; Barker and Thomas, 2004; Livermore et al., 2005). Evidence and causes of the Eocene/Oligocene event, based on extinction and survival patterns of foraminifera, were reviewed by Molina (2015, see other references herein). In order to establish the precise chronology of the turnover at the E-O transition, as the Priabonian and Rupelian stage stratotypes duration was imprecise, the International Commission on Stratigraphy 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 Planktic foraminiferal biostratigraphy, paleoecology and chronostratigraphy across the Eocene/Oligocene boundary in northern Tunisia Narjess Karoui-Yaakoub a, b Chaima Grira a, b Moncef Saïd Mtimet a Mohamed Hédi Negra b Eustoquio Molina c, [email protected] a Département des Sciences de la Terre, Faculté des Sciences de Bizerte, Université de Carthage, Jarzouna, Bizerte, 7021, Tunisia b Unité de Recherche: Pétrologie Sédimentaire et Cristalline, Université de Tunis El Manar, Tunisia c Departamento de Ciencias de la Tierra & IUCA, Universidad de Zaragoza, E-50009, Zaragoza, Spain Corresponding author. Abstract The biostratigraphic analysis of the Eocene-Oligocene transition of the Menzel Bou Zelfa and Jhaff sections in northeastern Tunisia (Cap Bon peninsula) allows us to identify a continuous planktic foraminiferal biozonation. The following biozones were recognized: Globigerinatheka semiinvoluta Zone (E14), Globigerinatheka index Zone (E15), (Hantkenina alabamensis Zone (E16) of the upper Eocene and Pseudohastigerina naguewichiensis Zone (O1) of the lower Oligocene. A rapid mass 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 (Hantkenina alabamensis, Hantkenina brevispina, Hantkenina nanggulanensis and Cribrohantkenina lazzarii), which mark the Eocene/Oligocene boundary. These species were tropical and subtropical surface and intermediate dwellers, with distinctive morphologies (carinate turborotalids and spinose hantkeninids), which were well adapted species of k-strategy. The surviving planktic foraminifera species were quite similar in morphology with globular chambers (globigerinids) and small planispiral (pseudohastigerinids), which were opportunistic species of r-strategy. The recognition of a 4 m thick interval, between the extinction of turborotalids and hantkeninids, indicates that the section is continuous and one of the most expanded throughout the Eocene-Oligocene transition. This section could serve as an auxiliary section (hypostratotype) for the complete definition of the Global Stratotype Section and Point for the Eocene/Oligocene boundary, which mark the base of the Rupelian Stage. Keywords: Planktic foraminifera; Eocene/Oligocene; Biostratigraphy; Paleoecology; Chronostratigraphy; Tunisia

1 Introduction - zaguan.unizar.es · The Eocene-Oligocene (E-O) transition was an epoch of great turnover, in both terrestrial and marine environments. Mammals were highly affected

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Page 1: 1 Introduction - zaguan.unizar.es · The Eocene-Oligocene (E-O) transition was an epoch of great turnover, in both terrestrial and marine environments. Mammals were highly affected

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,∗

[email protected]

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

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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.

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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

Page 4: 1 Introduction - zaguan.unizar.es · The Eocene-Oligocene (E-O) transition was an epoch of great turnover, in both terrestrial and marine environments. Mammals were highly affected

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

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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

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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

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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.

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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

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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

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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.

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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

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AcknowledgementsWewouldliketothanktheresearchunitteam“Pétrologiesédimentaireetcrystalline”oftheFacultyofSciencesofTunis.ThisstudyreceivedfinancialsupportandassistancethroughProjectCGL2014-58794P

fromtheSpanishMinistryofScienceandTechnology(FEDERfunds)andtheConsolidatedGroupE05fromtheGovernmentofAragón.

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QueriesandAnswersQuery:Thecitations“AmamiHamdi,2014;BenIsmail-Lattrache(1981);Wadeetal.,2004;Berggrenetal.,2005;AmamiHamdi,2014”havebeenchangedtomatchtheauthorname/dateinthereferencelist.Pleasecheck.Answer:Ok

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WadeB.S.,HoubenA.J.P.,QuaijtaalW.,ChoutenS.,RosenthalY.,MillerK.G.,KatzM.E.,WrightJ.D.andBrinkhuisH.,Multiproxyrecordofabruptsea-surfacecoolingacrosstheEocene-OligocenetransitionintheGulf

ofMexico,Geology40(2),2012b,159–162.

Highlights

• PlankticforaminiferaE14,E15,E16,O1ZonesareidentifiedacrosstheE/Oboundary.

• ThesectioniscorrelatedwithothersinTanzania,SpainandtheE/OGSSPinItaly.

• TurborotalidsandhantkeninidsunderwentarapidmassextinctionacrosstheE/O.

• TheextinctioneventattheE-Otransitionisrecordedinaveryexpandedinterval.

• TheTunisiansectionisaverysuitableauxiliarysectionfortheE/Oboundary.

Page 15: 1 Introduction - zaguan.unizar.es · The Eocene-Oligocene (E-O) transition was an epoch of great turnover, in both terrestrial and marine environments. Mammals were highly affected

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