Río Antas, Almería, Spain

20 Pages·2015·5.62 MB·English

Clim.PastDiscuss.,11,3897–3936,2015 D
www.clim-past-discuss.net/11/3897/2015/ isc
doi:10.5194/cpd-11-3897-2015 us
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©Author(s)2015.CCAttribution3.0License. io
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Thisdiscussionpaperis/hasbeenunderreviewforthejournalClimateofthePast(CP). p
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The MIS 5 palaeoenvironmental record in D
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the SE Mediterranean coast of the Iberian s
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Peninsula (Río Antas, Almería, Spain) P
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T.Torres1,J.E.Ortiz1,A.M.Blázquez2,B.RuizZapata3,M.J.Gil3,T.Martín3,
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andY.Sánchez-Palencia1
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1LaboratoryofBiomolecularStratigraphy,E.T.S.I.MinasyEnergía,UniversidadPolitécnica c
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deMadrid,C/RíosRosas21,Madrid28003,Spain ss
2EnvironmentalandMarineSciencesResearchInstitute,CatholicUniversityofValencia ion
C/GuillemdeCastro94,46003Valencia,Spain P
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3Dpto.Geología,FacultadCiencias,UniversidadAlcaládeHenares,CampusUniversitario, pe
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UniversidadAlcalá,28871AlcaládeHenares,Madrid,Spain
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Received:13July2015–Accepted:12August2015–Published:26August2015
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Correspondenceto:J.E.Ortiz([email protected]) is
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PublishedbyCopernicusPublicationsonbehalfoftheEuropeanGeosciencesUnion. ss
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3897 |
Abstract D
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LandwardsofaMIS5bar,aboreholecore(SRA)wasanalyzedtoestablishtherelation- s
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ship between the lagoonal record and the raised beach deposits in the surroundings io
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oftheAntasrivermouthandtoreconstructthePleistocenepalaeoenvironmentalevo- P
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5 lutionofthesouthernMediterraneancoastoftheIberianPeninsula.63sampleswere pe
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recoveredforaminoacidracemizationdating,86samplesforsedimentologicalandpa-
leontological determination, 37 samples for pollen identification and 54 for biomarker |
analysis.AARrevealedthattheboreholerecordcontainsMIS11,MIS6andMIS5de- D
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posits, the latter extensively represented. During the end of MIS6 and MIS5, a sand c
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10 barrier developed and created a shallow lagoon with alternating terrestrial inputs this ssio
process being common in other Mediterranean realms. Litho- and biofacies allowed n
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the identification of distinct paleoenvironments through time, with the presence of a a
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lagoonal environment alternating with alluvial fan progradation. Biomarkers indicated e
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constant input from terrestrial plants, together with variable development of aquatic
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macrophytes.Thepalynologicalcontentallowedthereconstructionofthepaleoclima-
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tologicalconditionsduringMIS6and5,withevidenceofsevenscenarioscharacterized is
byalternatingaridandrelativelyhumidconditions. cu
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1 Introduction P
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In many areas of the Mediterranean coast – Spain, Morocco, Tunisia – the current
morphologyappearsasaseriesofcliffswhereAlpinetectonics-linkedparallelranges |
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reachtheseaalternatingwithlagoonsandwetlands.SomeoftheQuaternarycoastal D
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deposits of the Spanish Mediterranean realm have been studied, mostly focusing on c
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raised marine deposits and addressed faunal remains and radiometric ages (Goy et ss
al., 1986; Hillaire-Marcel et al., 1986; Causse et al., 1993; Zazo, 1999; Zazo et al., ion
2003; Dabrio et al., 2011) and amino acid chronology (Hearty, 1986, 1987; Hearty et P
25 a
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al.,1986;Torresetal.,2000a,2010a;Ortizetal.,2004a).Unfortunately,raisedmarine e
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depositsofferlimitedpaleoenvironmentalinformationbecausetheircoarse-verycoarse D
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grain size does not allow the preservation of most paleobiological (pollen, ostracods c
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andforaminifers)andgeochemical(biomarkers)signals. ss
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Other authors have examined the lagoonal records (Collado and Robles, 1983; n
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5 Usera et al., 2002, 2006; Ferrer et al., 2005; Blázquez and Usera, 2010; Ferrer y a
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Blázquez, 2012) and pollen content of continental sequences (Pérez-Obiol and Julià, e
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1984;FumanalandDupré,1986;BurjachsandJulià,1994;Ylletal.,1994;Badaland
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Roiron, 1995; Carrión and Dupré, 1996; Carrión and van Geel, 1999; Carrión et al.,
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1999). is
10 In this regard, the lagoonal record in the Antas river mouth area and associated cus
raisedmarinedepositsprovideaninterestingsystemtoestablishmethodologicalwork s
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whichallowtheunderstandingofhighstandsealeveldepositsthrough-timeevolution n
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intheMediterraneanrealm,especiallyMIS5. a
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The Mediterranean coastline between the mouths of the Aguas and Antas rivers er
hasnotbeenexaminedindetail.Anumberofraisedmarinedepositswerepreviously
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sampledforthedeterminationofaregionalamino-stratigraphicalframework(Torreset
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al.,2000a,2010a).Thelagoonaldepositsthatoutcropinthisareahavebeenstudied is
byPantaleón-Canoetal.(2003),whoanalyzedthepollencontent,butthebizarre14C cu
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agesobtainedprecludedanyrealisticinterpretationoftherecord.In2007,anew25m io
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20 borehorecore(namedSRA)wasdrilled. P
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Coastal marshes and mires, most representing the last evidence of the satellite p
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basins that developed after the Alpine Orogeny Period, hold the best preserved pa- r
leoenvironmental signals. Lagoonal and marsh deposits appear along the Spanish |
MediterraneancoastinPeñíscola(Useraetal.,2006),Torreblanca(ColladoandRob- D
les, 1983; Segura et al., 1997), Almenara (Blázquez and Rodríguez-Pérez, 2013), is
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Jávea(Fumanaletal.,1993;Useraetal.,2002),GandíaandLaSafor(Viñals,1995a), s
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Moraira (Viñals, 1995b), Albufereta-Alicante (Ferrer et al., 2005, Ferrer y Blázquez, io
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2012),andRoquetasdeMar(PantaleónCanoetal.,2003).However,allthesedeposits P
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haveshortsequencescoveringtheHolocene.WhilelongerPleistocenesequencesap- p
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pearintheElcheBasin(Blázquez,2005,BlázquezandUsera,2010)andPegoBasin D
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(Dupré et al., 1988; Mateu, 1989; Viñals et al., 1989; Hernández-Ruiz et al., 1993; c
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Viñals and Fumanal 1995; Viñals, 1996; Mateu et al., 1997; Torres et al., 2013), se- ss
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quences belonging to MIS5 are present as loosely cemented sands. Consequently, n
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5 thecorerecoveriesarelowandthegrainsizeisnotfavorableforpaleoenvironmental a
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recording. e
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Wethereforeconsideredthisdepositsuitableforinterpretingthepaleoenvironmen-
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talevolutionofthesouthernMediterraneancoastoftheIberianPeninsula.Theaimsof
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thisstudywereasfollows:(1)toestablishthechronologicalframeworkthroughamino is
10 acidracemizationdatingofthelagoonaldeposits(SRAcore);(2)toobtainpaleoenvi- cus
ronmentalinformationbasedonsedimentologyandmicropaleontologyofalongMIS5 s
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sequence; (3) to determine regional plant biomes and paleoclimatic variations based n
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onpollendata;and(4)toaddressthebiomesoftheareabyinterpretingthebiomarkers a
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containedinthesediments. er
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2 Geographicalandgeologicalsetting D
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2.1 Geographicalandphysiographicalframeworkofthestudyzone s
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The SRA borehole was drilled in the Vera Basin, which is an inverted basin (Stokes, P
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2008)intheInternalZoneoftheBeticCordillera.TheGarruchavillageisplacedona p
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hillslopecappedwithbeachdepositsofPleistoceneagelyinguncomfortablyonquasi-
azoic Pliocene delta sediments. The western side of the village ends abruptly due to |
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averticalcliff,whichfallsonaflat,almostendorheic,depression–ElSalar–inwhich D
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salinemudsaccumulateduringflash-floodepisodesthattheAntasrivercannotdrain, c
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asoccurredon28September2012. ss
This area around the mouths of the Aguas and Antas rivers hosts a series of ion
25 Pleistocene-agemarinedepositsthatmarktheeasternedgeofthemarineVeraBasin Pa
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(Fig.1),whichcanbeage-correlatedinspiteoftheyweresubjectedtostrongneotec- D
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tonicprocesses(Torresetal.,2000a,2006,2010a,2013). c
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Infact,intheimmediateneighborhoodoftheSRA,astriperepresentinganancient ss
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barriersystem(MIS5)andrunningparalleltothepresentdaycoastlineisclearlyvisible n
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5 in Fig. 1. This stripe consist of gravel and coarse sands that are strongly carbonate- a
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cemented,andshouldprotectthelagoonalareaofSRAduringMIS5.Thesematerials e
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appearasforeshoredippingbedssomedecimetersthick.Atsomepoints,anumberof
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bedsdipbackshore.ScatteredGlycymerissp.shellsarevisible,aswellassomerare
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Persististrombuslatus(sin.Strombusbubonius)representatives.Todaytheancientbar is
10 is occupied by a tourist center, but a section is still visible on each side of the road cus
enteringtheresort. s
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2.2 BiologicalsettingoftheareaaroundtheAntasriver a
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Theareaisplacedinthe“almeriense”sectorofthe“murciano-almeriense”chorological
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province(RivasMartinez,1988).Thenativeplantspeciesareresistanttodroughtand
aridity,whichoccurduringthesummerandalsoinsomewinter-autumnmonths.Thus D
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plant species have xerophytic characteristics, thus largely exposing soil and bed rock c
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(FerréBueno,1979). s
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ThenaturalvegetationintheAlmanzoravalleyfallsintheclimaticdominionofQuer- n
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cusilicisandOleo-Ceratonion.TheformerholdsQuercusilex,Q.coccifera,Juniperus a
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phoenicea,DhapnegnidiumandRetamasphaenocarpa,althoughQ.ilexisscarce.In e
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many areas, Pinus halepensis has disappeared or remains as scattered individuals,
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andinwetterzonesisolatedindividualsofP.pinasterarefound.Ingeneral,onlysub-
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serial bushes belonging to the Q. ilex dominion are present: Rosamarinus officinalis, is
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Cistusalbidus,Rhamnuslyciocides,Genistaumbelata,Ulexsp.,andR.spaenocarpa. u
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25 In more severely degraded areas, only species of Thymus, Artesania glutinosa and sio
Stipatenacissimaaredetected. n
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In the western-most sierras, a variety of the Q. ilex grade was observed: the sub- a
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grade Q. lusitanica-Acer monspesulamun granatensis attesting a wetter and colder r
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climate. Towards the eastern ends of the sierras there was a gradual change to the D
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Oleo-Ceratoniongrade,representedbyQ.coccifera,Pistacialentiscus,Ceratoniasili- c
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qua,Oleaoleaster,andP.halepensis. ss
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All these series showed profound degradation, which is linked to industrial activity n
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5 (miningandmetalworkingindustry),agriculture,andgrazing(RodríguezAriza,1999). a
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3 Materialandmethods |
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ThesamplingworkfocusedontheSRAoftheAntasriver(Fig.1).Thisboreholewas is
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drilled for geotechnical studies on the right margin of the river, near its mouth, where s
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theriverincises3.5mintosoftmaterials. io
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10 TenkilometersupstreamoftheAguasrivermouth,thetufadepositsfromAlfaix(ALF) Pa
outcrop.ThesewereusedonlytochecktheresultsobtainedinSRA.Thetufadeposits p
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consist of a 23m thick sequence (Schulte et al., 2008), the bottom of which is 7m r
above the present day Aguas river thalweg. Using U/Th dating, these authors dated |
thelowermost13m(approx.)ofthesequenceat169 9kaandreportedthatitshows D
15 afluvialcharacter,theuppermostpartcomprisingas±eriesofpiled-upbioconstructed iscu
tufabarrierstrappingfluvialanddominantslopedeposits.Thetopofthesequenceis s
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108ma.s.l.andisdatedat>26 1ka(Schulteetal.,2008). ion
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3.1 AARanalysis p
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ToestablishthechronologyoftheSRArecord,weselectedostracodshellsastheypro- |
20 videdexcellentresultsinformerstudies(Ortizetal.,2004b,2009).Similarly,ostracods D
werealsosampledinthreelevelsoftheAlfaixfluvialterrace. is
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Ostracodspecimensfromvariousspecieswererecovered,althoughonlyCyprideis s
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torosa representatives were included in the analysis because it was the only species io
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present in all horizons. Only in one horizon of the SRA borehole (15m depth) were P
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Herpetocypris reptans representatives also collected. Thus, analytical samples from p
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each bed contained only single monospecific C. torosa valves, except for SRA-1500. D
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Whenpossible,weperformedsevenanalysesofthesamebed.Atotalof63analytical c
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samplesfrom11horizonsoftheSRAborehole,and16analyticalsamplesfromthree ss
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bedsoftheAlfaixfluvialterracewereexamined(Table1). n
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5 Ostracodvalveswerecleanedsonicallyindistilleddeionized(DDI)waterandrinsed a
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in the same water to remove sediment. Some valves were also cleaned with a small e
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brush under a binocular microscope to eliminate fine debris. In order to remove sec-
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ondary organic molecules adsorbed to the shells, the valves were then submerged
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in 3% hydrogen peroxide (H2O2) for 2h following Kaufman (2000) and Hearty et is
10 al.(2004). cus
Amino acid concentrations and ratios were quantified using HPLC, following the s
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sample preparation protocol described by Kaufman and Manley (1998) and Kauf- n
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man (2000). This procedure involves sample hydrolysis, which was performed under a
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anN2 atmospherein7µLof6MHClfor20hat100◦C.Thehydrolysateswereevapo- er
ratedtodrynessinvacuo,andthenrehydratedin7µL0.01MHClwith1.5mMsodium
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azide and 0.03mML-homo-arginine (internal standard). Samples were injected in an
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Agilent-1100 HPLC, equipped with a fluorescence detector. Excitation and emission is
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wavelengthswereprogrammedat335nmand445,respectively.AHypersilBDSC18 u
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reverse-phasecolumn(5µm;250 4mmi.d.)wasusedfortheanalysis. io
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20 Derivatization took place before injection by mixing the sample (2µL) with the pre- P
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columnderivatizationreagent(2.2µL),whichcomprised260mMisobutyryl-L-cysteine p
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(chiral thiol) and 170mM o-phthaldialdehyde, dissolved in 1.0 M potassium borate r
buffer solution at pH 10.4. Eluent A consisted of 23mM sodium acetate with 1.5mM |
sodiumazideand1.3microMEDTA,adjustedtopH6.00with10Msodiumhydroxide D
and 10% acetic acid. Eluent B was HPLC-grade methanol and eluent C consisted of is
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HPLC-grade acetonitrile. A linear gradient was performed at 1.0mLmin−1 and 25◦C, us
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from95%eluentAand5%eluentBuponinjectionto76.6%eluentA,23%eluentB, io
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and0.4%eluentCatmin31. P
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For the age calculation of SRA and ALF samples, aspartic acid and glutamic acid D
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werechosenbecausetheyaccountforoverca.50%oftheaminoacidcontentinmost c
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ostracod valves (Kaufman, 2000; Bright and Kaufman, 2011). The numerical age of ss
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eachbedwasdeterminedbyintroducingtheasparticacidandglutamicacidD/Lvalues n
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5 obtainedinC.torosaindividualsfromtheAlfaixterracesandtheSRAboreholeintothe a
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agecalculationalgorithmsdescribedbyOrtizetal.(2004b).Theageofasinglebedis e
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theaverageofthenumericaldatesobtainedforeachaminoacidD/Lvaluemeasured
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inostracodsfromthathorizon.Theageuncertaintyisthestandarddeviationofallthe
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numericalagescalculatedfromtheaminoacidD/Lvaluesofeachlevel. is
10 We used the age calculation algorithms obtained in ostracods collected in central cus
and southern Spain by Ortiz et al. (2004b) for the dating these deposits because a s
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similar thermal history can be inferred for these areas, as they are all located in the n
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MediterraneanclimaticzoneoftheIberianPeninsula,withasimilarmeanannualtem- a
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perature. Likewise, the age calculation algorithms were established for the ostracod er
species analyzed here (C. torosa and H. reptans), which show similar racemization
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rates for Middle and Lower Pleistocene localities (Ortiz et al., 2013). Thus DL ratios
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aredirectlycomparablewithoutanyconversionfactor. is
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3.2 Sedimentology sio
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Atotalof86samplesat20–30cmintervalswerepickedfromtheboreholecore.These a
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samples were analyzed for sedimentological, micropaleontological (especially, ostra- e
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coda and foraminifera) and palynological studies. The sampling interval was chosen
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onthebasisofmajorchangesinsedimentcolor,grainsize,andthepresenceofchem-
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icals(gypsumcrystals),andmacrofossils. is
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Totally dried samples were gently crushed, soaked, passed through a 62µm mesh u
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25 sieve,andanalyzedundermicroscope.Somesampleswereresin-embeddedtostudy sio
thesandfractionmineralogyinathinsection. n
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3.3 Palynology D
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A total of 37 samples were selected for palynological analysis. Pollen was extracted s
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followingstandardprotocols(Couteaux,1977;Faegrietal.,1989;GirardandRenault- io
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Miskovsky,1969;Mooreetal.,1991).Theresidualswerepollen-enrichedthroughflota- P
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5 tioninThoulet’sdenseliquor(GoeuryandBeaulieu,1979)andlaterplacedinEppen- pe
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dorftubesandpreservedinglycerin.
Pollen grains were read and counted following Cambon (1981): 42 rows in each |
sample.Thenumberofpollengrainsinthesamplesoscillatedbetween110and716, D
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although in some samples the number was so low (10–20) that they appeared in the c
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10 pollen diagram as “presences”. In these cases the number of identifiable taxa was ssio
greatlyreduced(5orlower). n
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Statistical analysis was done using the package OLEA (M. Arroyo unpublished), a
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whichisbasedonphilosophyoftheTILIA® andTILIA-GRAPH® (Grimm,1987,1992) e
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packages.
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Inthesampleswithastatisticallysignificantnumberofpollengrains,webuiltAP/NAP
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logs and analyzed the rarefaction (Birks and Lyne, 1992) to determine vegetation di- is
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versity. u
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Inordertofacilitatetheinterpretationofthedata,webuiltasyntheticpollinicdiagram, sio
whichincludedthemostsignificanttaxa(Pinus,Juniperus)inthespectrum,aswellas n
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20 thelargesttaxaclusters(Mesophilous,Mediterranean,Xeric,Steppic). ap
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Finally, all the sampled were subjected to a PCA (Principal Component Analysis) r
usingtheBiplotapplicationfromExcel-Microsoft. |
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3.4 Biomarkeranalyses is
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Atotalof54sampleswerecollectedforbiomarkeranalysis,coarse-grainedsediments s
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25 beingdiscarded.5gofsedimentpersamplewasdriedat50◦Cfor24handthenground nP
withamortarandpestle.Biomarkerswereextractedinanacceleratedsolventextractor a
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(DionexASE200)usingdichloromethane/methanol2:1at1500psiand175◦C(after er
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various tests, this temperature proved to be the optimum for the extraction of most D
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biomarkers).Theheatingphaselasted8minandthestaticextractiontime5min. c
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Theisolatedlipidextractwasconcentratedtodrynessusingarotaryevaporator,then ss
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methlylated with trimethylsilyldiazomethane and methanol for 20min and evaporated n
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5 with nitrogen. Samples were redissolved in 1 ml of dichloromethane prior to analysis a
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bygaschromatography(HP6890)withamassselectivedetector(HP5973)equipped e
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withanATM-5column(250 0.25mm;0.20µm).Heliumwasusedasthecarriergas.
Theoventemperaturewasp×rogrammedfrom60to300◦Cat6◦Cmin−1andtheinjector |
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wasmaintainedat275◦C.ComponentswereidentifiedwiththeDataAnalysisprogram is
10 and the Wiley mass spectral Library: n-alkane distributions were obtained from the cus
GC/MSchromatogramsofm/z57.Wefocusedourstudyonn-alkanes,thoughacids sio
andketoneswerealsoidentified. n
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4 Results
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4.1 Chronology D
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15 The D/L values of aspartic acid and glutamic acid in the ostracod samples from the ss
Alfaix tufa terraces and the SRA borehole are shown in Table 1. The ages obtained io
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in theformer werecoincident with those reported bySchulte etal. (2008) usingU/Th P
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dating(169 9and148 8ka),althoughthestandarddeviationofAARagesobtained p
± ± er
herewaslarger.
SRA ages, in agreement with Alfaix U/Th-dated tufa deposits, totally differed from |
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the ages described by Pantaleón-Cano et al. (2003) for the lagoonal deposits of the D
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mouthoftheAntasRiver,namely:8690 150yrat22m,7730 100yrat11mdepth, c
± ± u
8070 90yr at 10m, 8210 250yr at 6.3m, 6280 60yr at 5.8m. A single criticism ss
of the±se data is that the a±ges, although supposed±ly not linked to laboratory errors ion
25 in dating, are erratic because the sedimentation rate is unrealistic. According to our Pa
experience in Pego basin (Torres et al., 2013), these anomalous 14C values can be pe
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explained as recent contamination associated with ground-water circulation in near- D
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shore aquitards in arid areas under a marine intrusion regime. In fact, the analysis of c
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totalcarboninbulksedimentsisinappropriatebecausesignificantdifferencesbetween ss
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the radiocarbon content of the bulk sediment and true age can arise (Olsson, 1986; n
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5 MacDonald et al., 1987; Lowe et al., 1988; Brown et al., 1989; Torres et al., 2010b). a
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Pantaleón-Canoetal.(2003)datedasampleat0.5mofdepthat1390 100BP;how- e
± r
ever, although appearing reliable, it seems somewhat too young as implies that the
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deepriverincisionshouldoccurredinhistoricaltimes.
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The possibility of ostracod reworking from older deposits is unlikely because the is
10 shells were not eroded, in some cases still being articulated. Furthermore, in some cu
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samplesostracodswerefoundtogetherwithjuvenilethin-shelledCerastodermaglau- s
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cumrepresentativesthatweretoofragiletobetransported. n
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The AAR dating of the SRA record allowed us to determine that MIS11 (a single a
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datingwasobtained),MIS6pro-parte,andMIS5arerepresented.Astheagesshowed er
an uncertainty of about 25%, the MIS5 sub-episode boundaries were refined on the
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basis of the palynological analysis and paleoenvironmental information derived from
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sedimentology. This implies that MIS6-MIS5e was displaced 80cm upwards, and we is
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wereunabletodifferentiatebetweenMIS5bandMIS5a. u
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4.2 Sedimentologyandfossilcontent n
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TheSRAcorecomprisedmainlymaterialofdetritalorigin,predominantlyclay,silt,and e
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marls(Fig.2).Sixlithologieswereobserved:
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– Gm:GravelC=26–60mm(poorlyrecoveredfromthecore),withclastsofquartz, D
dolostone, limestone and metamorphic rocks, with variable amounts of hetero- isc
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metricquartzsand,abundantmicaflakes,andred-brownlutites(matrix?). s
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– Gf: fine-grained gravel (C=5mm) made of quartz and metamorphic rocks in a
25 P
lutiticmatrixwithlimonitizedbotroids(derivedfrompyrite),inwhichreworkedma- ap
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rinemicrofossilswerecommon. r
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– Sl:laminatedmedium-coarsegrainedquarztsands,withmetamorphicrockfrag- D
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ments. In outcrops, ripples and scattered charcoal fragments are visible. This is c
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theonlyportionoftherecordvisibleonoutcrops. ss
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– Fs:carbonatedsandylutites(silt),withscarcescatteredsandgrains,locallyiron P
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oxide-stained. p
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– Fm: massive lutites (clay), with small amounts of fine-grained sand. Mica flakes
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areabundant.
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– Mg:white-graymarlswithlenticularandtabulargypsumcrystals,limonitizedplant c
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stemsandcarbonate-cementedtubuli(plantroots?). ss
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The mineralogy of the fraction coarser than 62µm (Table 2) confirmed that the lo- P
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cal source of the sediments was metamorphic rocks (micaschists) and dolostones of pe
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Permo-Triassic age. The former are reflected in a myriad of mica flakes and quartz
grains, most of them reworked from Pliocene marine silts and marls, as attested by |
large amounts of resedimented foraminifers from this age. There was a very small D
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15 contributionofmaficvulcanitesofNeogeneage. cu
Many samples contained foraminifers, with the exception of the following levels: ss
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2300, 1780–1600, 1330–1240, 790, 1120–850cm. We separated the foraminifera n
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species into two assemblages: autochthonous and allochthonous associations. The a
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formerholdsindigenousspecimenswhilethelatterindicatesreworkedtestsfromolder e
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strata(Pliocene).Mostofthesamplesincludingforaminifersshowedtheallochthonous
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association. Only levels 2300, 1850, 1390–1360, 1180, 820, 700, 300–240cm con-
tainedautochthonousforaminifers,thefollowingbeingcommon:Elphidiumexcavatum D
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(Terquem),Ammoniatepida(Cushman),Haynesinagermanica(Ehrenberg).Otherau- cu
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tochthonousforaminifersincludedAubignynaperlucida(Heron-AllenandEarland),El- s
io
phidiumwilliamsoniHaynes,BuliminamarginataD’Orbigny,andBolivinasp. n
25 P
The allochthonous association comprised planktonic (Globigerinoides ruber a
p
(D’Orbigny), Orbulina universa D’Orbigny, Globigerinoides sacculifer (Brady), Glo- er
3908 |
bigerinoidesobliquusBolli,Globigerinabulloides;D’Orbigny)anddeepbenthonic(Mel- D
is
onis pompilioides (Fichtel and Moll), Pullenia bulloides (D’Orbigny), Cibicides sub- c
u
haidingeri Parr, Cibicides pseudoungerianus (Cushman), Legenina sp., Cancris au- ss
io
ricula (Fichtel and Moll), Amphicorina scalaris Batsch, and Globocassidulina oblonga n
P
5 Reuss.)foraminifers,togetherwithsomeshowingwidebathymetricdistribution(Bulim- a
p
inamarginataD’Orbigny,Ammoniabeccarii(Linné),andNonioncommune;D’Orbigny). e
r
This association is typical of Pliocene age and consistent with findings by Torres et
|
al.(2000b).
D
This association was present between 2960 and 2840cm, but foraminifer tests did is
10 notshowevidenceofreworkingandthereforecouldbedatedasPliocene. cus
Alargenumberofostracodvalveswererecoveredfromalmostallthesamples,the s
io
presence of C. torosa being continuous along the entire length of the borehole. In n
P
general,thevalveswerewell-preserved.Thisspeciesisfoundinhighlysalinemarshes, a
p
lagoons,andcontinentalponds,inwaterswithawiderangeofsalinity,varyingfrom0.5 er
to 60‰ (De Deckker, 1981). However, according to Carbonnel (1983), this ostracod
15 |
hasbeenfoundinwaterswithsalinityupto140‰.Theseobservationsimplythatthe
D
valves reflect a wide range of hydrogeochemical conditions. Other ostracod genera, is
c
includingH.reptansandIlyocyprisbradyiSars,typicalofwaterbodieswithlowsalinity u
s
s
(De Deckker, 1981), were also recovered, together with C. torosa in some samples io
n
20 (1500,1420,7000,and540cm). P
a
Mollusks were scarce in the SRA and limited to levels 1390–1330cm, in which p
e
Cerastoderma sp. and Hydrobia sp and other bivalves were present. Likewise, we r
foundbivalvesandgastropodsbetween550and520cmandalsoidentifiedcontinental |
gastropodsat330cm. D
is
c
4.3 Biomarkers u
25 s
s
io
Lagoons and marshlands receive organic matter from autochthonous (phytoplank- n
P
ton,bacteria,aquaticmacrophytes)andallochthonous(terrestrialplantdebris,pollen) a
p
e
sources. Consequently, palaeoenvironmental changes are reflected in the biogeo- r
3909 |
chemistryofsedimentrecords(MeyersandIshiwatari1993;Meyers1997,2003).How- D
is
ever, the interpretation of organic geochemical signals is not always straightforward c
u
becauseinmostcasesorganicmatterisamixtureofcomponentsfrommanysources ss
io
andwithvariabledegreesofpreservation. n
P
5 n Alkanes are among the biomarkers most commonly used. These compounds a
− p
havetheadvantagethattheyarelesssusceptibletomicrobialdegradationthanother e
r
typesoforganicmatterbecausetheylackthefunctionalgroupsthatconferchemicalre-
|
activity,andalsothattheyhavelowwatersolubility(PrahlandCarpenter,1984;Meyers
D
et al., 1995). The n-alkanes present in sediments reflect mainly the contribution from is
10 algae,bacteria,aquaticmacrophytes,andlandplants.Severaln-alkaneratioscanbe cus
usedforpaleoenvironmentalreconstructionpurposes. s
io
Thelogsofthevariousindexesrelatedtothen-alkanecontent,namelythen-alkane n
P
predominant chain, the average chain length (ACL), the aquatic macrophyte proxy a
p
(Paq), the Terrigenous/Aquatic Ratio of hydrocarbons (TARHC), and the relative per- er
centages of C , C and C with respect to the sum C + C + C , are shown in
15 27 29 31 27 29 31 |
Fig.3.
D
The SRA cores samples showed n-alkanes with an odd-over-even carbon number is
c
predominance, with a chain length distribution ranging mainly from C to C . We u
17 31 s
s
detectedanoverwhelmingdominationofC31 n-alkane(44over54samples),butin10 ion
20 ofthesesamplestheC21 homologwaspredominant. P
a
The ACL (Poynter, 1989), calculated as [(Ci×i+ Ci+1×(i+1) + Ci+2×(i+2)... + pe
C n))/( C+C +...+C ),withi=13,n=33],showedfewoscillations(Fig.3), r
n× i i+2 n
withvaluesvaryingbetween21.9(15.9cm)and28.0(640cm). |
P
The Paq index, calculated as the (C23+ C25)/(C23+ C25+ C29+ C31) ratio (Ficken D
etal.,2000),allowsdiscriminationbetweentherelativecontributionofaquaticmacro- is
25 c
u
phytesandterrestrialplants.Paqvaluesregisteredseveraloscillations,butwithalow s
s
range,fallingbetween0.05(150and240cm)and0.25(790cm). io
n
P
a
p
e
r
3910 |
Sillimanetal.(1996)reportedthattheterrigenous/aquaticratio,calculatedas(C + D
31 is
C29+C27)/(C15+C17 +C19),distinguishesbetweenterrestrialplantandalgalinputs. cu
s
TheTAR indexvariedbetween39.9(40cm)and1.4(1660cm). s
HC io
Then-alkanecompositionasrelativepercentagesofC ,C andC withrespect n
27 29 31 P
5 to the sum C27+ C29+ C31 showed some oscillations (Fig. 3), but in all cases, the ap
relativepercentageofC31accountedformorethan50%ofthen-alkanespresent,with er
amaximumat760cm(70%).
|
4.4 Palynology D
is
c
u
Pollenwasnotpresentinthelowermost(2850–1830cm)oruppermost(280–0cm)part ss
io
10 oftheSRArecord. n
P
In the samples from the remaining record, we identified 39 taxa, of which 11 were a
p
trees(Pinus,Juniperus,Corylus,Betula,Juglans,Quercusdeciduous,Olea,Quercus e
r
evergreen Alnus, Fraxinus and Ulmus), 6 bushes (Calluna, Ericaceae, Myrtus, Cis-
|
taceae,Pistacea,andRosaceae),and22grasses(Asteraceaeliguliflorae,Asteraceae
tubuliflorae, Poaceae, Sanguisorba, Artemisia, Chenopodiaceae, Ephedra, Plantago, D
15 is
Polygonaceae,Rubiaceae,Rumex,Urtica,Apiaceae,Brassicaceae,Caryophyllaceae, cu
s
Fabaceae, Boraginaceae, Scrophulariaceae, Asphodellus, Potentilla, Rhamnaceae s
io
and Violaceae). Also, we detected two aquatic species (Cyperaceae and Alisma). n
P
Monolete and trilete sporae and 15 non-pollinic microfossils (NPMs) from various a
p
20 affinities were also found: 3b type (Pleospora) of dry character, 55A (Sordaria) 113 er
(Sporomiella), 368 (Podospora) and Riccia of coprophilic affinity, as well as the
|
mesoeutrophic types 181 and 731 and the eutrophic 170 type (Rivularia). We also
D
detecteddeforestation-linkedtype207(Glomuscf.fasciolatum)andsoilerosion-linked is
c
Pseudoeschizaeaecircula. u
s
s
25 The pollen assemblage reveals a Mediterranean climatic scenario with fluctuations io
n
ofmoistureand,insomeintervals,mainlyintheupperhalfofthesection,thepresence
P
ofNitrophiloustaxa. ap
e
r
3911 |
The pollen diagram (Fig. 4) reveals that tree cover was denser in the lower part of D
is
therecordandmoreopenatthetop.Similarly,theshrubbystratumdidnotcontribute c
u
greatlytothevegetationstructurenordidNPM,aquatictaxa,ormostoftheelements ss
io
identifiedinthetreesorgrassesgroups. n
P
5 Given the above observations, we built a synthetic diagram taking in considera- a
p
tion various taxa (Pinus, Juniperus) and associations of trees (Mesophilous, Mediter- e
r
ranean), grasses (Xeric, Steppic and Nitrophilous), NPM type 3b, and Coprophilous
|
taxa(Fig.5).
D
is
c
u
5 Discussion s
s
io
n
10 5.1 Sedimentaryenvironments Pa
p
e
WedifferentiatedthefollowingfivelithologicalunitsintheSRAboreholeonthebasisof r
sedimentological characteristics and microfossil content (Fig. 2): Unit I (29.7–28.2m: |
Pliocene yellow-grey marls and silts; Unit II (28.2–24.2m loosely cemented gravels D
interbeddedwithsandsofPleistoceneage);UnitIII(24.2–18.2.2mlooselycemented is
c
u
15 Pleistocene gravels and sands); Unit IV (18.2–3.0m variegated lutites with bioclasts ss
andgypsum);andUnitV(3.0–0.0mlaminatedfine-grainedsands).Becauseofsome io
n
minorvariationsinlithologyandbiologicalcontent,UnitIVwassub-dividedinten(a–j) P
a
sub-episodes. p
e
r
AlthoughPantaleón-Canoetal.(2003)identifiedtheseunitsintheirboreholerecord,
theyobservedpeatdepositsbetween22.50andca.20.60mthatwerenotpresentin |
20
theSRAcore.Thoseauthorsdidnotprovidethecoordinatesoftheirborehole,however, D
is
this discrepancy allows us to conclude that SRA and Pantaleón-Cano et al. (2003) c
u
boreholesweredrilledindifferentareasofthepaleo-lagoon. ss
Eachsedimentaryunitcorrespondedtoacertainenvironment(Table3,Fig.2).With ion
25 theexceptionofmarineconditionsthatoccurredduringthePliocene,thebasinshowed Pa
p
evidenceofalluvialfanprogradationalternatingwithlagoonalandpalustrineepisodes. e
r
3912 |
ThealternationofthesecycleswasespeciallycommonduringMIS6and5,reflecting D
is
environmentalchangesthatdonotnecessarilycoincidewithclimatechangesinferred c
u
fromthepalynologicalinterpretation.Thesedeviancescanbeexplainedbyoffsetbe- ss
io
tweenclimateandsedimentologicalresponse. n
P
5 Thus, the Pleistocene record of the SRA borehole was deposited during two peri- a
p
ods (Table 3, Fig. 2): the lowermost sands belonging to Units II and III corresponded e
r
to MIS11, whereas the lutites of Unit IV (uppermost 16m) belonged to the end of
|
MIS6 and MIS5, the latter fully recorded. The stratigraphical hiatus corresponding to
D
theMIS11-MIS6periodexplainsthedistinctgeomechanicalcharacteristicsofthetwo is
10 deposits (cemented and compacted vs. uncemented and water-soaked). These units cus
canbecorrelatedwithbeachandbardepositsofthesameage. s
io
During MIS11 alluvial fan conditions were predominant in the Vera Basin. Thick n
P
massive gravels in the lower half of the record, followed by silts with short palustrine a
p
episodes(autochthonousostracods)canbeidentifiedasfantoesediments.Wewere er
unabletodetermineothepaleoenvironmentalconditionsbecauseofthelackofpollen
15 |
grains.
D
NomarinerecordfromMIS6wasfoundonland,butmarinegeologymapping(Díaz is
c
delRíoandFernándezSalas,2005)ofthearearevealedalong,widestripofcoarse u
s
s
sand at a depth of 60–70m, which may represent an undated lowstand system track io
n
20 LST(MIS6?). P
a
We consider the AAR ages obtained for the MIS6 deposits feasible. The lower half p
e
of the record identified the margin of a playa lake which, in the upper half, changed r
to the red-brown silty sediments of a mud flat. According to the pollen record, the |
playa lake deposits correspond to dry-cold (relatively) conditions followed by humid D
and temperate-warm ones. During the deposition of the mud flat, cool and dry con- is
25 c
u
ditions dominated. Although MIS6 showed markedly unfavorable climatic conditions, s
s
as in other areas of southern Iberia, this period was a “climatic amelioration” when io
n
comparedwithMIS5. P
a
p
e
r
3913 |
5.2 Organicgeochemistry(biomarkers) D
is
c
u
Ashortdescriptionofthen-alkaneindicesusedisgiveninTable4.n-Alkanecontent s
s
provided reliable information on the local distribution of plants, thus completing the io
n
moreregionaldataprovidedbypollenanalysis. P
a
5 The predominance of the C31 n-alkane in most of the samples indicated the main per
input of grasses along the whole record (Fig. 3). Levels maximizing in the C ho-
21
molog can be linked to aquatic macrophyte dominance, usually associated with the |
presenceofaquaticfaunaremains(ostracodsand/orpelecypoda),asoccurredinsub- D
is
unitsIV-a(1690),IV-c(1390,1360),IV-e(820,790)andIV-i(550,520).However,Unit c
u
10 II (2840), Unit III (2050) and sub-unit IV-b did not hold faunal remains (Fig. 2). In all ssio
casesephemeralshallowwatermassesappeartohavedeveloped. n
P
The variations in Average Chain Length (ACL) values were small, although some a
p
clarificationscanbemade.Inthisregard,theACLvaluesoscillatedbetween21.9and e
r
28.0,implyingareducedcontributionoflowmolecularweightn-alkanes,usuallylinked
|
to algae and bacteria. However, the ACL values were slightly lower in Units II, III and
15
D
subunitsIV-aandIV-b,indicatingagrowthofaquatictaxa. is
Thedominanceoforganicmatterderivedfromterrestrialplantsoveralgaeinputcan cu
s
alsobeinterpretedfromtheTARHC index,whichshowedvalueshigherthan1.5inall sio
cases,beinghigherthan3.0in80%ofthesamples. n
P
The Paq values were originally defined and used to determine the relative contri- a
20 p
e
bution of macrophyte taxa and terrestrial plants to some African lakes (Ficken et al., r
2000).AccordingtoFickenetal.(2000),Paqvaluesunder0.1arelinkedtoadominant
|
contributionfromlandplants,whilevaluesbetween0.1and0.4reflectsignificantinputs
D
fromemergentmacrophytes.Paqvalueshigherthan0.4aretypicalinsedimentswith is
c
a major n-alkane input of submerged/floating macrophytes. In the SRA record, most u
25 s
s
ofthesamplesshowedPaqvaluesbetween0.05and0.25,indicatingamajorinputof io
n
terrestrialplantsandemergentmacrophytes.Theabsenceofsubmergedmacrophyte P
a
dominanceindicatesthatthewatermasswaslimitedintimeanddepth. p
e
r
3914 |
In agreement with the lowest ACL values observed in the lower half of the record D
is
(UnitsII,IIIandsub-unitsIVa–b),Paqvalueswerebetween0.1and0.26,suggesting c
u
aconsiderablecontributionofemergingmacrophytes.Incontrast,intheupperhalfof ss
io
therecord,mostofthesamplesshowedPaqvalueslowerthan0.1,linkedtoterrestrial n
P
5 plants, with the exception of five excursions to higher values linked to a major input a
p
fromemergingmacrophytes(samplesfrom970,910,790,520and300cm).Episode e
r
V showed a greater terrestrial input, which can be explained by its alluvial character,
|
withfloatingterrestrialplantdebrisstillvisibleattheincisedriverbanks.
D
TherelativepercentageofC31 withrespecttothesumC27+C29+C31 showedcer- is
10 tainoscillations,thusallowingustodiscriminatetheoriginofn-alkanefromterrestrial cus
sources.Apercentagegreaterthan50%reflectsgrass-originpredominance.However, s
io
weestablishedthreesubtlezoning: n
P
a
– Althoughtherecordshowedgrassdominance,threedominionswereclearlydif- pe
r
ferentiated: Episode IIto Episode IV-b (2840–1360cm)showed a saw-tooth dis-
tributionwithamaximum-minimumrangeof10%. |
15
D
– Between sub-episodes IV-c and IV-h the relative percentage of C was higher is
31 c
u
than in the first described dominion, its top being abruptly marked by the lower- s
s
most %C reached in the SRA record, coinciding with sub-unit IV-i (marls with io
31 n
Cerastodermasp.). P
a
p
20 – Sub-episodeIV-jandEpisodeVshowedoscillatinglowervaluesoftheindex. er
|
5.3 Palynology
D
is
Analysis of the evolution of the pollen frequencies allowed us to distinguish seven (I- c
u
s
VII) climate-related phases in the synthetic diagram (Fig. 5). Unfortunately, due to a s
io
lackofpollengrainsinsedimentsbelongingtoMIS11,paleoenvironmentalconditions n
P
25 couldnotbeestablished. ap
e
r
3915 |
InPhaseI(1850–1700cm),thepollencontentwaslow,althoughPinusandPoaceae D
is
werepresent.Towardsthetop,thepresenceofMediterranean,Xeric,andNitrophilous c
u
taxaincreasedandthendecreaseddramaticallyattheendofthisphase,favoringthe ss
io
presence of Juniperus. We interpret these observations as an initial warm and dry n
P
5 climate,turningtoacoldone,asattestedbythedevelopmentofJuniperus. a
p
Phase II (1700–1550cm) began with a sharp decrease in the presence of Junipe- e
r
rus, which favored the growth of Mesophilous taxa and later Mediterranean species,
|
the frequencies of Xeric and Steppic taxa being low. Nitrophilous taxa increased and
D
scatteredsamplesofAquatictaxaappeared.Weinterprettheseclimaticconditionsas is
10 temperate-warmandhumid. cus
InPhaseIII(1550–1330cm),therewasacleardominanceofPinus,followedbyXeric s
io
andSteppictaxaand,toalesserextent,NitrophilousandNPM-3Btaxa.Weinterpret n
P
thesedataasindicativeofadryandcolderperiod,asattestedbythelowdevelopment a
p
ofMesophilousandMediterraneantaxa. er
In Phase IV (1330–1120cm), there was a clear expansion of Mediterranean taxa,
15 |
withsomeoscillations,togetherwithanincreasingpresenceofXericandSteppictaxa,
D
aswellasJuniperustowardsthetop,markingatemperatureincreaseunderdrycon- is
c
ditions. u
s
s
InPhaseV(1130–840cm),MediterraneanandMesophiloustaxaclearlydominated, io
n
20 thoughwithsomeoscillations.TherewasacleardeclineinthepresenceofPinus,and P
a
Juniperus disappeared. At the beginning of this phase the presence of Aquatic and p
e
Nitrophilous taxa increased and in the upper part they were replaced by Xeric taxa r
and NPM-3b, ending with a short period in which the pollen content was practically |
absent.Weinterprettheseobservationsasindicatingawarmperiodthatwasinitially D
relativelyhumidandthatevolvedtowardsdryconditions;thisphasecanbecorrelated is
25 c
u
withMIS5e. s
s
Phase VI (840–700cm) started with an increase in Juniperus and Steppic taxa, io
n
which were later substituted by Mediterranean and Mesophilous ones. The presence P
a
p
e
r
3916 |