Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 www.elsevier.nl/locate/palaeo The Abad composite (SE Spain): a Messinian reference section for the Mediterranean and the APTS F.J. Sierroa,*, F.J. Hilgenb, W. Krijgsmanc, J.A. Floresa aDepartmentofGeology,UniversityofSalamanca,37008,Salamanca,Spain bDepartmentofGeology,FacultyofEarthSciences,UtrechtUniversity,Utrecht,TheNetherlands cPaleomagneticLaboratory“FortHoofddijk”,UtrechtUniversity,Utrecht,TheNetherlands Received7July1999;acceptedforpublication28August2000 Abstract Ahigh-resolutionintegratedstratigraphyispresentedfortheAbadmarlsoftheSorbasandNijarbasinsinSESpain(pre- evaporitic Messinian of the Western Mediterranean). Detailed cyclostratigraphic and biostratigraphic analyses of partially overlappingsubsectionswereneededtoovercomestratigraphicproblemsinparticularencounteredatthecomplextransition fromtheLowertotheUpperAbad.TheresultingAbadcompositesectioncontainsacontinuousstratigraphicrecordfromthe Tortonian/Messinian boundary up to the transition to the Messinian evaporites of the Yesares Member. All together, 18 calcareous plankton events were recognized which were shown to be synchronous throughout the Mediterranean by means of detailed (bed-to-bed) cyclostratigraphic correlations. The magnetostratigraphy allowed the identification of the four magneticreversalsofchronC3AnintheUpperAbad.DetailsinthesedimentarycyclepatternsallowedtheAbadcomposite tobeastronomicallycalibrated.Thiscalibrationtothe658NsummerinsolationcurveofsolutionLa90 yieldedastronomical (1,1) agesforallsedimentarycycles,calcareousplanktonbioevents,ashlayersandpaleomagneticreversals.Uptonow,theAbad composite is theonly astronomicallywell-calibrated section thatprovided a reliablecyclostratigraphy, magnetostratigraphy andcalcareousplanktonbiostratigraphy.Assuchitwillserveasareferencesectionbothforthepre-evaporiteMessinianinthe MediterraneanaswellasfortheMessinianintervalintheAstronomicalPolarityTimeScale.q 2001ElsevierScienceB.V.All rightsreserved. Keywords:Biostratigraphy;Magnetostratigraphy;Milankovitch;Planktonicforaminifera;Mediterranean;Messinian 1. Introduction 1987;LangereisandHilgen,1991;Krijgsmanetal., 1995, 1997). Detailed cycle pattern analysis have During the last decade, high-resolution biostrati- allowed these sections to be tuned to astronomical graphic,magnetostratigraphicandcyclostratigraphic target curves, resulting in astronomical time scales studies of marine sections in the central and eastern forthePlio-Pleistocene(Hilgen1991a,b;Lourenset Mediterranean have provided an excellent chronos- al.,1996)andthelateMiocene(Hilgenetal.,1995). tratigraphicframeworkforthelateNeogene(Hilgen During the late Messinian, however, restricted environmental conditions in the Mediterranean caused a widespread deposition of evaporites, * Corresponding author. Tel.: 1923-29-4497; fax: 1923-29- preceeded by cyclic alternations of diatomites and 4514. E-mailaddress:[email protected](F.J.Sierro). marls (e.g. Tripoli Formation of Sicily). These 0031-0182/01/$-seefrontmatterq2001ElsevierScienceB.V.Allrightsreserved. PII: S0031-0182(00)00253-4 1 4 Atlantic 2 Ocean Perales MConatseindoel C EvaporiteRsoadto MolinoMsoBlinosA A B SpainMediterranean Sicily S F CAablacdarenite rboas RiverAguas FalconaraCrete FManeetroocmhieani .J.Sie r r o e t a Neogenesediments l. Volcanicrocks / Basement Sorbasbasin P MolatasB MolatasA MessinianReefs ala e o g Gypsum e o Gqyupasrurmy quarrGyyBpsum RoadtoNijar Nijarbasin graphy,Pa quarryA Almería lae o c 0 10 MediterraneanSea lim a to HighwaytoMurcia log RoadtoMurcia LaHuelga y, P a N340 Herrerías la Sorbas e o ElTesoro ec o RoadtoAlmería lo g y 1 6 8 RoadtoPeñasNegras (2 RAarmejbolsa BASEMENT Gafares nPeegñraass Gafarillos 001) section 1 4 Cuevadel 1 Gafares Pajaro ElSbaaljtoador –169 Polopos Cortijada Arejos Cortijada Almendral Gafares Arejos section HighwaytoAlmería RoadtoNijar RamblaSaladilla RamblaGafares Evaporites Abadmarls Calcarenites Fig.1.Locationmapofthesectionsstudiedinthispaper:(above)SectionsoftheSorbasbasin;and(below)SectionsoftheNijarbasin. F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 143 typesofsedimentsaredifferentfromthehemipelagic 2.General setting and stratigraphy deposits of Pliocene and early Messinian age and have until recently hindered the construction of an TheSorbasandNijarbasins(Fig.1)aresmallLate astronomical time (polarity) scale for the late Neogene depressions that evolved in the Eastern Messinian. Betics (SE Spain) in a structural corridor that was Recently,ithasbeenshownthatthecyclicbedding subjected to compressional and extensional events of the pre-evaporitic diatomites is related to astro- (Montenat and Ott d’Estevou, 1996). During the late nomically controlled variations in regional climate Tortonian, a general uplift caused an important sedi- as well (Hilgen et al., 1995; Sprovieri et al., 1996b; mentary discontinuity in both basins (Weijermars Sierro et al., 1997, 1999; Krijgsman et al., 1999; et al., 1985; Martin and Braga, 1996), separating Hilgen and Krijgsman, 1999; Vazquez et al., 2000). middle–upper Tortonian hemipelagic and turbiditic Up to now, however, no section has provided a reli- sediments from the uppermost Tortonian–lower able and continuous magnetostratigraphic record. Messinian pre-evaporitic deposits (Ott d’Estevou TripolisectionsfromSicilyrevealasecondary(over- 1980; Van de Poel, 1991; Martin and Braga, 1996). printed) normal magnetisation (Langereis and The pre-evaporitic sequence starts with calcarenitic Dekkers,1992)orshowcontroversialresults(Gautier deposits of latest Tortonian age (Azagador member, etal.,1994;McClellandetal.,1997).Sectionsinthe Vo¨lk 1964), overlying the middle–upper Tortonian Northern Apennines (Italy) are subject to diagenetic sediments or, unconformably, the basement. These overprintingandstrongtectonicdeformation(Krijgs- calcarenites of the Azagador member rapidly grade manetal.,1997;NegriandVigliotti,1997),whilethe upward into marls, clays and diatomites of early Metochia diatomite section on Gavdos (Greece) is Messinian age, generally classified in the literature overprinted by a secondary reversed component as the Abad member (Vo¨lk and Rondeel, 1964). The (unpublished data). baseoftheAbadmemberusuallyconsistsofayellow- To date, the Abad marls of the Sorbas and Nijar ishsiltyunitofseveralmetersthickness,whichcanbe basins in Southeast Spain are the only cyclically- regardedasatransitionalfaciesbetweentheAbadand bedded stratigraphic unit in the Mediterranean that Azagador. may provide a reliable magnetostratigraphy for the TheAbad marls, deposited inrelatively deep parts pre-evaporiticMessinianfromtheTortonian–Messi- oftheSorbasandNijarbasins,usuallyinterfingerand nian boundary to the base of the evaporites. Gautier gradelaterallyandverticallyintoplatformcarbonates et al. (1994) reported the first magnetostratigraphic and reefs (Cantera member, Vo¨lk 1964) that grow data from the Sorbas basin, correlating the Abad along the margins in shallower waters (Dronkert and marlstochronsC3Bn,C3Ar,C3AnandC3r(Gilbert Pagnier, 1977; Ott d’Estevou, 1980; Dabrio et al., Chron) and the evaporites (Yesares member) to the 1985; Martin and Braga, 1990, 1994, 1996; Braga lower part of chron C3r. The cyclostratigraphic and Martin, 1996). Several studies have identified an potentialoftheAbadmemberwasfurtherevaluated upwardchange,bothinsedimentaryfaciesandmicro- by Sierro et al. (1997, 1999), showing that the sedi- paleontologiccontent,allowingtheAbadmarlstobe mentarycyclicitywascontrolledbytheastronomical dividedintotwodistinctunits.(Geerlings1977;Dron- precession cycle. kertandPagnier,1977;Civisetal.,1979;Ottd’Este- The Abad member is therefore suitable for estab- vou, 1980; Van de Poel, 1991; Sierro et al., 1997, lishinganastronomicalpolaritytimescale(APTS)for 1999;Vazquezetal.,2000).TheLowerAbadischar- thecrucialperiodoftimethatheraldstheonsetofthe acterisedbyanalternationofinduratedhomogeneous Messiniansalinitycrisis(seeKrijgsmanetal.,1999). whitishmarlsandsofterhomogeneousgreymarlsrich This study mainly focuses on the elaboration of an in planktonic foraminifera. Grey-brownish laminated integrated stratigraphy for the Abad Member, which sediments,hereafterreferredtoassapropels,areonly will be used to establish a standard chronostrati- interbeddedinitsuppermostpart.TheUpperAbadis graphicframeworkbothforthepre-evaporiticMessi- recognised in the field by its brownish colour and is nian of the Mediteranean as well as for the late characterised by the intercalation of sapropels and Messinianinterval ofthe APTS. indurated diatom-rich (diatomites) layers containing 144 F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 more benthic foraminifera and plant remains. These middle part of the Upper Abad (Civis et al., 1979; diatomites are faintly laminated at the base and Gonzales Donoso and Serrano, 1977; Geerlings, strongly laminated (paper shales) towards the top. 1977;VandePoel,1991;Sierroetal.,1993;Gautier, AnothercharacteristicoftheUpperAbadistheinter- etal.,1994).Thislattereventhasbeenwidelyrecog- calationofverythinlaminaeofdistalsandyturbidites nisedthroughouttheMediterraneanbelowtheLower within the sapropels, indicating increasing grain-size Evaporites,orthelaterallyequivalentCalcarediBase interrestrialinput into the basins. (Zachariasse,1975;Colalongo,etal.,1979;Sprovieri, During deposition of the Lower Abad, sedimenta- et al., 1996a,b). Furthermore, a general impoverish- tionwascontinuousinmostareas.However,thelimit ment of the microfauna is observed immediately betweentheLowerandUpperAbadismarkedeither preceding the evaporite deposition in the Mediterra- byahiatusnearthemarginsorbysedimentinstability, nean (D’Onofrioet al., 1975). as evidenced by several slumps (multiple-slump BoththeAbadmarlsinthecentralpartofthebasins event) that transported Lower Abad relicts into andtheCanteramemberalongthemarginsareover- UpperAbadmarls,depositedinthebasindepocenters. lainbymassivegypsumdepositswithlaminatedpeli- The sedimentary instability was probably due to ticintercalations(Yesaresmember,Ruegg1964).The tectonic uplift of the basin margins, creating steep Yesares member is commonly correlated with the slopes that favoured sediment sliding into the deeper Lower Evaporites of the Central Mediterranean regions. In the Sorbas basin, the tectonic activity (Mu¨llerandHsu¨,1987;Gautieretal.,1994;Clauzon started during deposition of the upper part of the et al., 1996; Krijgsman et al., 1999), although some Lower Abad (i.e. from cycle LA17 upwards) but authors have proposed a correlation with the Upper was intensified at the onset of the formation of the Evaporites (Martin and Braga, 1994; Riding et al., Upper Abad. This tectonic event might be the same 1998, 1999). asthe onethatcauseda regional unconformityalong the basinal margins (Martin and Braga, 1994, 1996). 3. Sections studied Messinian reefs of the Cantera member lie uncon- formably above the Azagador and lowermost Abad. Four sections (Molatas, Molinos, Gypsum quarry, This unconformity was caused by erosion of all, or Perales)intheSorbasBasin(Fig.1)andtwo(Almen- part,ofthe Lower Abadalongthebasinmarginsand dral,Gafares)intheNijarBasinwerestudiedtoobtain mighthaveextendedtowardsthebasincentres,where a continuous and complete record of the Abad sedimentation was only interrupted by the sliding of member, i.e. from the top of the calcarenites to the several repetitive slumps. A second slump is located base ofthe evaporites. in all Upper Abad sections of the Sorbas basin. This slumpcouldberelatedtotheunconformitythatsepa- 3.1. Sorbas basin ratesthebiohermunitfromthefringingreefunit,two marginal facies of the Upper Abad according to TheMolatassectionisacompositeof2subsections Martin and Braga (1994, 1996). exposed along the old road from Sorbas to Nijar, TheAbadmarlshavealwaysbeenconsideredtobe between Km 6 and 7 on the southern side of the Rio ofearlyMessinianageandbelongtotheGloborotalia Aguas (Fig. 1). Molatas A is a short subsection that mediterraneaandGlobigerinamultilobasubzonesof covers the yellowish silts overlying the calcarenite D’Onofrioetal.(1975)(Iaccarinoetal.,1975;Civiset and the lowermost part of the Abad marls. Molatas al., 1979; Gonzales Donoso and Serrano, 1977; Van B extends from the top of the yellowish silts and dePoel,1991;Sierroetal.,1993).ThebaseoftheG. comprises mostofthe Lower Abad (Fig. 4). mediterranea subzone was recognized near the base TheMolinossectionislocatedonthenorthernside of the Abad marls (Gonzales Donoso and Serrano, of the Rio Aguas, 500m north of Molatas, and also 1977; Sierro et al., 1993, 1996). The limit between comprises two subsections. The base of Molinos A the G. mediterranea and G. multiloba subzones was starts immediately above the multiple-slump event approximately correlated with the coiling change in that marks the limit between the Lower and Upper Neogloboquadrina acostaensis that occurred in the Abad (Figs. 2 and 4). Several white indurated layers F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 145 1a Molinos B 1b Molinos A 2 3 A U o 2 2 t A 9 U 2 8 o UA A2 A 4 t U U o t 4 23 U A UA 3 to TopofSlump A U 1c Gypsum Gypsum Slumps Abad Calcarenite 2 Perales A Perales C Perales B Gypsum UA23toUA34 LA13 LA15 LA17 UA4toUA22 Slump UA1 SapropelLA20 Slump LA18 to LA21 UA3toUA4 LA9 UA2 LA20 Slump LA17 Fig.2.PhotographsoftheMolinossubsections.1cPanoramicwiewshowingthecalcarenites(Azagadormember)atthebase,theAbadmarlsin themiddleandtheGypsumunit(Yesaresmember)ontop.ThelocationofsubsectionsAandBisalsoshown.1aand1b:Picturesshowingthe samplingtrajectoriesofsubsectionsAandBandthecyclesidentifiedineverysubsection.2:Photographshowingthesamplingtrajectoriesof thePeralessubsectionsA,BandC.Thegypsumunitisontopofthehill. 146 F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 Fig.3.Top:PhotographshowingthesamplingtrajectoriesoftheGafaressectionindicatingthedifferentintervalsbythecyclenumbers. Bottom.DetailedpictureoftheLowerAbadinGafaresshowingthecharacteristicalternationofinduratedlayersandhomogeneousmarls. CyclesLA11–LA15weresampledinthisgully. are present in the lower part while thin, well-lami- slumpunitinthetoppartofMolinosAasthestarting nated diatomites (paper shales) occur towards the point of Molinos B. In the latter section, a few very top.Becausetheupperpartofthissectionwascapped prominent paper shales are clearly visible in the byPlio-Pleistoceneconglomerates,wesampledMoli- weathered outcrop. Unfortunately, the uppermost nosB(nextgullytothenorthwest,Fig.2)tocomplete levels and the transition to the Gypsum are not well theuppermostpartoftheUpperAbad.Itwaspossible exposed. tocorrelatebothsubsectionsbylateraltracingofsome TheGypsumquarrysectionconsistsoftwosubsec- markerbeds.Wechosethedistinct,6.5mthick,upper tions lying on both sides of a tributary of the Rio F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 147 Aguas, immediately to the east and southeast of the showing the characteristic indurated layers (see maingypsumquarry(Fig.1).Gypsumquarrysection Fig. 3). This is the only section in which sedimenta- A shows yellowish silts at the base, immediately tion was continuous in the Lower to Upper Abad abovethetopofthecalcarenites(Azagadormember). transition, showing no evidence for slumping or These silts gradually pass upward into grey marls, hiatuses. The section has been extended to the recordingmostoftheLowerAbad(Fig.4).Insection base of the evaporites but the uppermost part is not B, the limit between the lower and Upper Abad is well exposed and shows clear indications of tectonic recorded by a sharp change in colour and lithology. deformation. TheUpperAbadisalmostcompletebutcyclebedding The Almendral section is found approximately is not clearly visible in the exposures because of 5km west of Gafares. It covers most of the Lower surface weathering. However, several prominent Abad and the lower part of the Upper Abad (Fig. 4). paper shales can be clearly distinguished in the ThelimitbetweentheLowerandUpperAbadisvery upper part of the gullies below the gypsum. Two sharp, suggesting the existence of a hiatus. Both the slump intervals were recognized: the first, of 1.5m, indurated layers as well as some thick sandstone is characterised by small-scale deformations in the layersinthelowerpartofthesectionareclearlyvisi- firstsapropeloftheUpperAbad;thesecondisclearly ble.SapropelsarealreadypresentintheLowerAbad visible in the upper part. Above the upper slump, buttheyaregreyincolour.TheUpperAbadcyclicity prominent paper shales are slightly folded indicating isevidentbuttheidentificationofseveralshearplanes tectonic deformation. Part of the succession, which parallel to the bedding prevented us from being contains two of the prominent paper shales, has certain about the cycle correlations. The Almendral even been tectonically doubled. This repetition was sectionisoverlainbyPlio-Pleistoceneconglomerates. confirmed by means of a detailed comparison with Some paper shales are visible near the top. Many the other Abad sections which provided an excellent small faults are present but individual layers can high-resolution control onthe cyclostratigraphy. readily betraced. The Perales section is located on the northern side of the Rio Aguas, approximately 2km north-east of the village ofLosMolinos(Figs.1 and2).Perales A 4.Cyclostratigraphy and tephrastratigraphy records part of the Lower Abad, while Perales B reveals the transition between the Lower and Upper In the Lower Abad sedimentary cycles are defined Abad, recording the multiple-slump event that by the cyclic occurrence of indurated layers interca- includes part of the Lower Abad in this section lated within the homogeneous marls (see Fig. 4). (Fig. 4). Two very thick and prominent sapropels These indurated layers are between 20 and 60cm that mark the base of the Upper Abad can easily be thick and are usually characterised by abundant tracedlaterallyalongthedifferentgullies(seeFig.2), Opal Ct (Sierro et al., 1997, 1999; Vazquez et al., indicatingthatsedimentationcontinuedinthispartof 2000). Because there are no sapropels in most of the the basin after each slump event. Perales C extends Lower Abad we used the bottom of the indurated fromtopofthemultiple-slumpeventtothebaseofthe layers as the lower limit of the cycles. Based on Evaporites. Although some small-scale deformation these criteria, we defined cycles LA1–LA21. In the was observed near the base of Perales C, sedimenta- UpperAbad,asapropeliticlayerappearsinthemiddle tion was continuous. partofthehomogeneousmarlsbetweentwoconsecu- tive indurated layers. We used the base of the sapro- pels to define the limits of the cycles to maintain the 3.2. Nijar basin samecriteriausedinotherMediterraneansapropelitic The Gafares section is located on the northern sections. Cycles UA1–UA34 were recognized in the margin of the Nijar basin near the village with the UpperAbad.Becauseofthischangeinthedenomina- same name, on the right side of the road from this tionofthecyclesbetweentheLowerandUpperAbad, village to El Saltador bajo (Fig. 1). In the Gafares cycleLA21andcycleUA1arepartiallythesame(see section,mostoftheLowerAbadisperfectlyexposed, Fig.4). 148 F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 149 In the lowermost part of the Abad, immediately usuallythin.Thecyclicsedimentationendswithcycle above the yellow silts, cyclicity is not evident, UA34, which is overlain by a transitional interval to althoughsomesections(e.g.MolatasAandGypsum the Gypsum, characterised by the presence of clays Quarry A) show indications of slightly more indu- and limestones. The transition to the Gypsum is rated layers alternating with homogeneous marls always poorly exposed and therefore cyclicity is not (Fig. 4). Cyclicity starts to be clearly discernible easily recognisable inthe field. with the occurrence of a first prominent indurated Three biotite-rich levels were identified in our layer that lies several metres above the base of the sections. The lowermost ash layer was found inme- marls. Because this is the first well distinguishable diately belowthe indurated layer ofcycle LA1. The lithological cycle in all sections, we termed it as middle ash layer was found within LA17. On top of Abad Cycle 1 (LA1) (Fig. 5a). It is followed by sapropelUA1twothinashlayersoflessthan0.5cm cycles LA2, 3 and 4, which are usually thinner than thicknessareseparatedbya2cmthickmarllayerin normal.IntheSorbasbasin,induratedlayersofLA9 section Perales, whereas up to 6 or 7 very thin andLA10arealwaysprominent,incontrasttoindu- biotite-containing ash layers are found in the corre- rated layer 11, which is usually thin. In the Nijar lative cycle in the Gafares section. These character- basin, this pattern is less clear. Cycle LA12 is the istic layers, together with the high-resolution thickest cycle, both in the Sorbas and Nijar basins. biostratigraphy, were very useful for the correlation The homogeneous marls of cycle LA15 is always of the sections in the complicated multiple-slump extremely thin and the homogeneous marls of cycle interval. LA16isalsolessthickthaninmostothercycles.The characteristic pattern of cycle LA15 and LA16 5.Biostratigraphy provides one of the most useful criteria for cyclos- tratigraphic correlations in the Lower Abad (see Biostratigraphy was mainly based on quantitative Fig. 4). In the Nijar basin (Almendral and Gafares and qualitative changes in the planktonic foraminif- sections),thefirstsapropeloccursinthemiddlepart eral assemblages (Figs. 5 and 6) although some of the homogeneous marls of cycle LA17. In the nannofossil results are presentedas well. Perales section, which is probably located near the depocenteroftheSorbasbasin,thefirstsapropelalso 5.1.Keeled globorotaliids occursincycleLA17.Inmoremarginalsettings(i.e. Molatas B), sapropels were not formed until cycle The groups of Globorotalia menardii (dex.) and (UA1) (LA21). Globorotalia miotumida (sin.) that play a keyrole in In the Upper Abad, cycles UA6 and UA7 have Mediterranean and Atlantic correlations were identi- distinct sapropels, while the sapropels of cycles fiedinalloursections.SpecimensofG.menardiidex UA5,UA9andUA11arepoorlydeveloped.Besides, wereonlyfoundinthelowermostsamplesoftheAbad cycleUA4ismuchthickerthanaverage.Higherinthe marls, inmediately above the top of the transitional succession, the very thin sapropel of LA13 and the yellowish silts (Figs. 4 and 5). The last occurrence thicker-than-average homogeneous bed of UA17 are (LO) of this group is followed 50cm upward by the characteristic. In the uppermost part, the sapropel of first regular occurrence (FRO) of the Globorotalia UA31 is a good marker because it is very thick and miotumida group (Figs. 4 and 5). Both groups do weaklylaminated.Incontrast,thesapropelofUA32is notcoexist in oursections. Fig.4.Cyclostratigraphicandbiostratigraphiccorrelationsofallsectionsstudiedinthispaper.1.LOoftheofthegroupofGmenardiidex.2. FrOoftheG.miotumidagroup.3.InfluxofthehighlyconicalformsoftheG.miotumidagroup.4.TopoftheparacmeofR.pseudoumbilicus.5. LAOofthegroupofG.scitulasin.6.StrongreductionofthegroupofG.scituladex.7.BottomacmeofthegroupofG.scituladex.8.Top acmegroupofG.scituladex.9.FAOofG.siphonifera.10.LastinfluxoftheG.miotumidagroup.11.LrOoftheG.miotumidagr.12.First abundantinfluxofT.multiloba.13.LastabundantinfluxofsinistralNeogloboquadrinids.14.FirstabundantinfluxofdextralNeogloboqua- drinids.15.ShortinfluxofthegroupofG.scituladex.16.InfluxsinistralNeogloboquadrinids.17.ShortinfluxofthegroupofG.scituladex. 18.Influx.sinistralNeogloboquadrinids. 150 F.J.Sierroetal./Palaeogeography,Palaeoclimatology,Palaeoecology168(2001)141–169 Fig.5.Abundancevariationofsomeoftheplanktonicforaminiferausedtodefinethemainbioevents.(a)FromthebaseoftheAbadmarlsto cycleA34.(b)FromcycleA34tothebaseoftheEvaporites.Magnetostratigraphyfromcycles1to20inferredfromKrijgsmanetal.1995and fromcycles20to55basedonthispaper(seeFig.7.Thiscompositeisbasedonthefollowingsections:MolatasA,MolatasB,MolinosAand MolinosB.LAG.menar.dex.(cid:136)LastoccurrenceofGloborotaliamenardiidextral.FrOG.miotum.Gr.(cid:136)Firstregularoccurrenceofthe Globorotalia miotumida group. R. Pseudoumbilicus(cid:136)Reticulofenestra pseudoumbilicus, LAO group G. scitula sin.(cid:136)Last Abundance OccurrenceofthegroupofGloborotaliascitulasinistral.Gr.G.scituladex.(cid:136)GroupofGloborotaliascituladextral.FAOG.obesa(cid:136)First abundantoccurrenceofGlobigerinaobesa.Lastr.Occurrence(cid:136)Lastregularoccurrence.Percentageofthedifferenttaxainrelationtototal planktonicforaminiferawiththeexceptionofthefirstcolumnin5bwhichshowsthepercentageofsinistralNeogloboquadrinidsinrelationto totalNeogloboquadrinid.