From the Mountain and the Sea: Provenance of the Stones of the Prehistoric La Pastora Tholos (Valencina de la Concepción, Seville, Spain)
Abstract
La Pastora tholos is the most complete and characteristic megalithic monument of the Valencina de la Concepción-Castilleja de Guzmán mega-site. This monument was built using three types of rock, each with different functions and coming from three different places: Paleozoic quartzarenite, granite, and Tertiary calcareous sandstone. A detailed petrological study of the rocks of the tholos and outcrops of similar rocks in the surroundings has been carried out, locating the possible source areas in areas at least 30 km to the N of the monument for the quartzarenite, 15 km for the granite, and 15 km to the S for the sandstone. Therefore, the community that built the monument has a high knowledge of the nature by, which allows them to locate these resources, and a sufficient social organization to exploit them and move them to the mega-site. In this sense, the layout of the outcrops suggests the possible use of boats or rafts to facilitate their displacement, or at least part of their movement.
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Minerals2024,14,194.https://doi.org/10.3390/min14020194www.mdpi.com/journal/minerals Article FromtheMountainandtheSea:ProvenanceoftheStonesof thePrehistoricLaPastoraTholos(ValencinadelaConcepción, Seville,Spain) LuisMiguelCáceres 1,2 ,TeodosioDonaire 1 ,SamuelRamírez‐Cruzado 3 ,JuanManuelVargas 4 ,FernandoMuñiz 5 , MónicaMartín 6 ,JoaquínRodríguez‐Vidal 1,2 ,FranciscoRuiz 1,2, *andLeonardoGarcíaSanjuán 3 1 DepartamentodeCienciasdelaTierra,UniversidaddeHuelva,Avda.TresdeMarzo,s/n, 21071Huelva,Spain;[email protected](L.M.C.);[email protected](T.D.);[email protected](J.R.‐V.) 2 CentrodeInvestigaciónenPatrimonioHistórico,CulturalyNatural(CIPHCN),FacultaddeHumanidades, UniversidaddeHuelva,Avda.TresdeMarzos/n,21071Huelva,Spain 3 DepartamentodePrehistoriayArqueología,UniversidaddeSevilla,C/DoñaMaríadePadilla, 41004Sevilla,Spain;[email protected](S.R.‐C.);[email protected](L.G.S.) 4 ServiciodeArqueología,AyuntamientodeValencinadelaConcepción,PlazadeEspaña9, 41907ValencinadelaConcepción,Seville,Spain;[email protected] 5 DepartamentodeCristalografía,MineralogíayQuímicaAgrícola,FacultaddeQuímica,Universidadde Sevilla,C/Prof.GarcíaGonzález,s/n,41012Seville,Spain;[email protected] 6 ÁreadeCienciasExperimentales,UniversidadC.E.U.CardenalEspínolaCEU, 41930Bormujos,Sevilla,Spain;monica.mart[email protected] *Correspondence:ruizm[email protected] Abstract:LaPastoratholosisthemostcompleteandcharacteristicmegalithicmonumentoftheValencinadelaConcepción‐CastillejadeGuzmánmega‐site.Thismonumentwasbuiltusingthree typesofrock,eachwithdifferentfunctionsandcomingfromthreedifferentplaces:Paleozoic quartzarenite,granite,andTertiarycalcareoussandstone.Adetailedpetrologicalstudyoftherocks ofthetholosandoutcropsofsimilarrocksinthesurroundingshasbeencarriedout,locatingthe possiblesourceareasinareasatleast30kmtotheNofthemonumentforthequartzarenite,15km forthegranite,and15kmtotheSforthesandstone.Therefore,thecommunitythatbuiltthemonumenthasahighknowledgeofthenatureby,whichallowsthemtolocatetheseresources,anda sufficientsocialorganizationtoexploitthemandmovethemtothemega‐site.Inthissense,the layoutoftheoutcropssuggeststhepossibleuseofboatsorraftstofacilitatetheirdisplacement,or atleastpartoftheirmovement. Keywords:geoarchaeology;megalithicmonument;LaPastoratholos;copperage;thirdmillennium BC;guadalquivirestuary 1.Introduction ThethirdmillenniumBCmega‐siteofValencinadelaConcepción‐CastillejadeGuzmán(henceforthValencina),locatedabout8kmwestofthecityofSeville,sitsonthe Aljarafeplateau,which,withadropofmorethan100m(even150matsomepointsof thesite),dominatesthecurrentfloodplainoftheGuadalquivirRiver.Thisfloodplainwas mostlyfloodedbyoceanicwaters[1,2]sincetheFlandrianmaximum,6500yearsago[3], andinsubsequentmillennia,constitutingamarineinletpartofwhichwasknowninRomantimesasLacusLigustinus. Thus,theCopperAgesiteofValencinawasinaprivilegedgeographicpositiondue toitslocation,topographicallydominatingthepalaeoestuaryoftheGuadalquivirandthe marinegulftheriveremptiedinto.Thisisverysignificantintermsoftheeconomicresourcesaswellastheconnectivityandcommunicationaffordanceslocallyavailableatthe Citation:Cáceres,L.M.;Donaire,T.; Ramírez‐Cruzado,S.;Vargas,J.M.; Muñiz,F.;Martín,M.; Rodríguez‐Vidal,J.;Ruiz,F.; GarcíaSanjuán,L.FromtheMountainandtheSea:Provenanceofthe StonesofthePrehistoricLaPastora Tholos(ValencinadelaConcepción, Seville,Spain).Minerals2024,14, 194.https://doi.org/10.3390/ min14020194 AcademicEditor:PaulinaFaria Received:18January2024 Revised:6February2024 Accepted:9February2024 Published:12February2024 Copyright:©2024bytheauthors. LicenseeMDPI,Basel,Switzerland. Thisarticleisanopenaccessarticle distributedunderthetermsand conditionsoftheCreativeCommons Attribution(CCBY)license (https://creativecommons.org/license s/by/4.0/).
Minerals2024,14,1942of16 time.InadditiontobeinglocatedonthesedimentaryterrainsoftheGuadalquivirbasin, whichareveryfertileforagriculture,itslocationwasalsostrategicduetoitsproximityto theSierraMorenaMountainrangeandallthenaturalresourcesthatthisregionhasto offer(multiplerockyandmineralmaterials,includingcopper,biomass,etc.).Asaresult, thedevelopmentofthesite(Figure1)reachedanextensionthatfarexceededthatofany othersitesatthetime:withc.460ha.[4],itisthelargestthirdmillenniumsiteintheIberian PeninsulaandWesternEurope[5]. Figure1.(A):Locationandextent(brown)oftheValencinamega‐siteandpositionofitsmainmegalithicmonuments:1:LaPastora;2:Matarrubilla;3:Montelirio;4:Structure10.042–10.049;5:Ontiveros(backgroundimagebyGoogleEarth).(B,C):ViewsoftheinteriorofLaPastoratholos:from theaccesstowardstheinterior(B)andfromthechambertowardsthecorridor(C). Thereiscurrentlynoconsensusontheinterpretationofthesite.Forsomeauthors,it isacontinuousandpermanentlysettleddwellingsite(avillage)withareasofspecializationindifferentmanufactures[6].However,otherauthorshavepointedtoreasonable doubtsastothetrueentityofthesite,interpretingitasanaggregationcenterthat,seasonallyandatcertainsymbolictimesorperiods,wouldbringtogetherthesurrounding communitiesduringthethirdmillenniumBC[5].Inanycase,thesocietythatoccupied thesitereachedahighdegreeofdevelopmentandsophistication. Proofofthecomplexityofthesiteandofthesocietythatinhabiteditarethemegalithicconstructionsthatarestillpreservedtoday,suchasOntiveros,Montelirio,LaPastora,Matarrubilla,andStructure10.042–10.049(Figure1).Inaddition,eachofthesemonumentshasitsowndistinctivecharacteristicsintermsofitsarchitectureandconstruction materials.Thus,forexample,LaPastoraandMatarrubillahavemasonrywallsandcapstonesmadeofsandstoneandgranite,butinMatarrubilla,itschamberisoccupiedbya largequadrangularmonolithicbasincarvedingypsum[7,8].Ontheotherhand,inMontelirioandOntiveros,thewallsareformedbyverticalorthostatsofshale,butthefirstone hastwochambers,andtheroofingwasachievedbymeansofdomesofsun‐driedmarl andclay[9].Foritspart,thestructure10.042–10.049issmallerandhasslateslabscovering thewallsbutwithoutsupportingfunction,neitherinthecorridornorinitstwochambers [10].
Minerals2024,14,1943of16 Thestudyofthegeologicalmaterialswithwhichthemegalithicmonumentswere builtisthefirststepintheirgeoarchaeologicalanalysis.Thisanalysisisbasicforthedeterminationofthesourceareas(i.e.,quarries)andtheestimationoftransportdistances. Withthisknowledge,itismorefeasibletoapproachthecharacteristicsofthesocietiesthat builtthem,includingtheirsocialorganization,worldview,knowledgeofthenaturalenvironment,andeventheirtechnicalcapabilities[11].Amongthesecapabilities,thoserelatedtotheextractionofrocksandtheirtransportareverysignificant,althoughitisnot alwayspossibletoobtaindirectdataontheseactivities.Wheneverspecificquarriescan beidentified,itispossibletolookforevidenceoftheextractionproceduresandtoolsused. Ontheotherhand,theevidenceofthemeansoftransportusedwillalwaysbemorelinked tospeculationandexperimentalteststhantothefindingofempiricalevidence. Geoarchaeologicalstudiesalongthelinesmentionedabovehavebeencarriedoutat majorworldsites,suchasStonehenge(GreatBritain)[12,13]orEasterIsland[14],providingfundamentaldataonquarryareasandrocktransport.IntheIberianPeninsula,where thousandsofmegalithshavebeendiscoveredandcatalogued,however,geoarchaeologicalapproacheshavebeenundertakenonlyinafewcases.TheseincludeLaChaboladela Hechicera,DolmendeAizkomendi,andPuigseslloses[15–18],inthenorth;ValeRodrigo, AntadaLajinha,andFreixo‐Redondo,inPortugal[19–21];ElPortilloininnerIberia[22]; andAlberite[23],PalacioIII[24],Panoría[25],ElPozuelo[26],andMenga[11]inthe south. RegardingValencina,characterizationstudiesoftherocksusedtobuildthetholoiof LaPastora,Matarrubilla,andMonteliriohavebeencarriedout[7,8,27],butadetailed analysisoftheprovenanceofthesematerialshasnotbeenaddressedsofar.Inthispaper, themainobjectivewillbetodeterminethesourceareasofthethreetypesofrocksusedto buildLaPastora,establishingtheminimumdistancestothedeposititself.Wewillalso suggestpossiblemeansandtypesoftransportthatcouldhavebeenused.Therefore,the studypresentedhereisgeoarchaeologicalincharacter,althoughitsapproachdiffersfrom thetraditionalcurrentsdevelopedbytheFrenchandAnglo‐Saxonschools[28].Themain aimofourworkislinkedtotheanalysisoftheorganizationofsettlementsattheregional level,basedonthedevelopmentofmodelsofresourceexploitationandmanagement.The resources,inthiscase,arethelithicelementsusedfortheconstructionofthemegalithic monumentofLaPastora. 2.LaPastoraTholos OfallthemajormegalithicmonumentscurrentlyknownattheValencinamega‐site LaPastoraisperhapsthemostrepresentative,complete,andleastaltered.Itisatholostypestructurewithalongcorridorandacircularchamberroofedbycorbellingtopped withamassivecapstone(Figure2).Theroofsofboththecorridorandthechamberare madeoflargestoneslabs,andthewholeiscoveredbyatumulusofloosematerials.In thiscase,thetumulusisverydegraded,butitisknowntohavereached,atleastatthe timeofitsdiscoveryin1860,amaximumthicknessofabout2m[29]. ThecorridorofLaPastorais44,36mlong,makingitthelongestofallIberianmegaliths,whileitsaveragewidthis1m,althoughitssectionisslightlytrapezoidal.Thiscorridorisdividedintothreesectionsthatareseparatedbyverticalandprotrudingorthostats,like“doors”withjambs,alintel(themiddle“door”),andathresholdstep(inthe accessintothechamber).These“doors”arepreservedbetweenthesecondandthirdsectionsandatthethresholdoftheentrancetothechamber.Ofthethreesectionsofthecorridor,thetwoclosesttothechamberareinperfectcondition,whilethefirst(themost external)doesnotpreservethecapstonecover.Thus,theheightinthesetwosectionsvariesfrom1.4to1.8m.Ontheotherhand,thechamberhasadiameterof2.6mandaheight of2.7m.Therefore,thetotallengthofthemonumentis46.96m[30].Anotherrelevant featureisitsorientationtowardssunset(243°),whichrunscountertothatofmostIberian megalithstowardssunrise[31].
Minerals2024,14,1944of16 LaPastorawasbuiltinauniformmanner,withnorecognizablephasing,distinctions, orlaterreconstructions.Theonlyalterationsarerecent,afteritsdiscovery,andofminor importance,suchasthenicheinthechamberandthespecificplacewhereitwasaccessed inthe19thcentury[30]. Themonumentisbuiltwiththreetypesofrocks(Figure2):quartzareniteinsmaller blocks,formingthedrymasonrywalls;largegraniteblocksusedascapstonesinthechamberandpartofthecorridor(sixpreservedintotal);andcalcareoussandstoneusedwith diversefunctionalities:inthetwoupperrowsofthechamberwall,capstonesinalarge partofthecorridor(20ofwhicharepreserved),jambs,lintels,andfloorslabs[7,8]. Figure2.LaPastorasection,capstones,andfloorplans,withthelithologyoftheirconstructiveelementsandnumberingofcapstonesandfloorslabsofthemonumentorderedfromtheentranceto thechamber.(modifiedfrom[8]). 3.GeologicalSetting LaPastoratholosisbuiltonsedimentsdepositedintheGuadalquivirBasin(Figure 3),oneofthemainCenozoicsedimentarybasinsoftheIberianPeninsula.IthasanENE toWSWelongatedtriangularoutline,withanapproximatelengthof360kmandabout 110kmonitsSWside.Towardsthenorthernmargin,thesedimentsareautochthonous andareunconformablydisposedonthePaleozoicrocksoftheIberianMassif,alargegeologicalunitthatoccupiesmostofthewesternIberianPeninsula.Onthesouthernmargin, sedimentarydepositsarerelatedtoorogenicactivityintheBeticCordillera[32,33]. ValencinaandLaPastoraarelocatedonthenorthernmarginoftheGuadalquivir Basin,wherethestratigraphicsequencepresentsthefollowinglithologiesfromthebase tothetop: (1) SandstoneandconglomerateswithcarbonatedcementdatebacktothelateTortonian [34]. (2) BlueMarlUnit[34]:marinegray‐greenishmarlfromtheMiocene(lateTortonian– Messinian). (3) Transitionfacies[35]:marlyclay,sand,andsandstonedepositedintheUpperMiocene.
Minerals2024,14,1945of16 (4) Pliocenesandandsilt[34]:yellowsandysiltwithcalcareousnodules(LowerPliocene),sandierandmorereddishupward. (5) Finally,theQuaternaryisbasicallymadeupofeolianandcoastalsandydeposits, fluvialsand,gravel,andmarshclay(Figure3). Figure3.GeologicalsettingofthesouthwestoftheIberianPeninsula,aroundtheValencinamegasite.Key:1:Devonianquartzarenitesandshales,thePQGroup;2:CarboniferousVolcanicSedimentaryComplex;3:Granitoid(SNSB);4:Basicplutonicrocks(SNSB);5:Carboniferousgreywackes andshales,theCulmGroup;6:Permianvolcanicandsedimentaryrock(PVB);7:Triassicclayand gypsum;8:Miocenemarl,sandstone,andflintstone;9:Tortoniansandstoneandconglomerate;10: Miocenemarl,BlueMarlUnit;11:TransitionFacies;12:Pliocenesandandsilt;13:Quaternarysand (dunesandbeaches);14:Quaternaryfluvialdeposits(conglomerate,sand,andclay);and15:marshland.Incolor,thegeologicalformationsfromwhichthestonesofLaPastoratholoscome(modified from[7]). About15kmnorthofValencina,theIberianMassifoutcropsextendwidelytothe eastandwest.TheIberianMassifisdividedintoseveralzoneswithdifferentlithological
Minerals2024,14,1946of16 andstructuralfeatures.Thus,inthestudysector,thesedimentaryrocksoftheGuadalquivirBasinweredepositedonthesouthernmostarea,namedtheSouthPortugueseZone (SPZ).ThiszoneisformedbyrocksfromtheUpperDevoniantothePermianandisdividedintovariousgeologicaldomains.TheIberianPyriticBelt(IPB)andtheSierraNorte deSevillabatholith(SNSB)arethedomainsthatcropoutinthisarea,aswellasvolcanic andsedimentaryformationsofthePermianViarBasin(PVB).TheIPBisfurthersubdividedintothreegroups[36,37](Figure3): (1) ThePhyllite–Quartzite(PQ)Groupisformedbyquartzarenitesandshalesoflate Devonianage. (2) TheVolcano–SedimentaryComplexhasapredominanceofvolcanicandsedimentaryrocksinterstratified,aswellasrocksofchemicalorigin.Thelargestmassive sulfidedepositsarelocatedinthiscomplex. (3) TheCulmGroupisformedbygreywackesandshales.TheageofthisandthepreviousgroupisCarboniferous. TherocksoftheSNSBintrudeintothepreviousformationsfromtheDevonictothe earlyCarboniferousandarecharacterizedbytheirabundanceandtypesofplutonicrocks, fromultramafic/mafictogranitoidrocks[38]. 4.MaterialsandMethods ThegeoarchaeologicalstudyofthestonesfromLaPastoratholoshasbeenapproachedfromtheperspectiveoftheircharacterizationandpetrographicanalysis.Petrographyisadisciplinethatstudiesrocksfromthepointofviewoftheirdescription,mineralogicalcomposition,andstructure.Thus,apetrographicstudyincludesavisualanalysis oftherockandadetailedpetrographicmicroscopicstudy.Inthisway,therocksarecharacterizedintermsoftheirarrangement,texture,mineralogy,organiccomponents,and classification.Withthesewell‐definedcharacteristics,itispossibletocomparesamples frommegalithswiththosefromrockoutcropstodetermine,basedontheirsimilarityor difference,thepossibleprovenanceofthestonesusedtobuildeachmonument. First,therockwasanalyzedasawholebydirectobservation,bothinthemonument andintheoutcropidentifiedasthemostprobablesourcearea.Inbothcases,thepropertiesconcerningtheappearance,fabric,generalcolor,texture,fossiliferouscontent,and mineralogyaredeterminedvisually.Ontheotherhand,structuralcharacteristics,includingitsdisposition,theexistenceandcharacteristicsofdiscontinuitiessuchasfractures, foliation,orstratificationsurfaces,aswellastherelationshipwithotherrocksinthesurroundingarea,areexaminedthroughfieldwork. Secondly,thinsectionsofrocksamplesfrombothmonumentandoutcropsarestudiedbypetrographicmicroscopy.Inthiscase,aNikonEclipseLV‐100POLpolarizedlight microscopeconnectedwithaNikonDS‐Fidigitalcamera(NikonInstrumentsInc.,Tokyo, Japan),availableattheLaboratoryoftheDepartmentofEarthSciences,Universityof Huelva(Huelva,Spain),hasbeenused.ThethinsectionsweremadeattheCentralLaboratoriesoftheUniversityofHuelvaandwereanalyzedunderplaneandcross‐polarized transmittedlight.Thisanalysisrevealstheshapeandsizeofthemineralsthatmakeup therock,thenatureoftheseminerals,theirabundance,thespatialrelationshipbetween them(texture),theexistenceandpercentageofthematrix,themicrostructure,microfossils,andawholeseriesofevaluableproperties.Inthisway,therockcanbeclassifiedand somespecificaspectsrelatedtoitsformationandevolutioncanbedetermined[39–41]. Therocksweresampledforthinsectionsdifferentlydependingonwhetherthey werefromthemonumentorthefield.Inthecaseofthelatter,ithasbeenpossibletoextract alargernumberofsamplesofgreatersize.Ontheotherhand,giventhemonument’s protectedheritagestatus,samplinghasbeenmuchmorerestricted.Looseornearlyloose fragmentsofLaPastorastoneshavebeentakeninmostcases,andalwaysininconspicuousareasofthemonument.Therefore,inthiscase,thesamplinghasnotbeenintensive, norhasitencompassedallthestonesofthemonument,although,overall,thesampling
Minerals2024,14,1947of16 achievedisconsideredsufficienttoaccountforthediversityofrocktypespresentinthe monument. 5.ResultsandDiscussion 5.1.PetrographyoftheLaPastoraStones Quartzareniteisthestonematerialusedinthemasonrywallsofthetholos(Figure2). Theyarenatural“bricks”,withcommonlyrhombohedralshapesandvariablesizesbutin thedecimetricrange(Figure4A).Theirfacesarenaturalandcorrespondtostratification, foliation,and/orjointingsurfaces.Theserockshavefineintercalationsofshales.Bothmaterialsshowhorizontalandcrosslaminations.Thinsectionsshowawell‐sorted,veryfinegrainedquartzareniteformedbyquartzand,toalesserextent,feldspars,whitemica, greenmica(chlorite?),andopaquemineralsincludedinasericiticmatrix.Theshaleintercalationshaveamineralogicalcompositionsimilartoquartzarenitebutwithagreater abundanceofsericite.Thealternationofquartzareniteandshalecanalsobeobservedin thinsections,aslayersoflightercolorandcoarsergrainsize(sandstone)andlayersof darkercolorandfinergrainsize(Figure4B). Figure4.Quartzarenite.(A):BlocksofthislithologyasmasonryinthewallsofLaPastora.(B):A representativethin‐sectionphotomicrographofablockfromthemonument.(C):OutcropofthePQ formationintheCuestadelaMediaFanegaarea.(D):Athinsectionofquartzarenitesinthelatter outcrop. Thegraniteslabsallappeartobefairlyhomogeneous,exceptforoneofthem,which hasanaplitedykeononeofitsedges(Figure2,capstonenumber8),resultinginaninterestingcontrastoftextureandcolor. Thestructureoftheseblocksismassive(Figure5A),andthetextureunderthemicroscopeisequigranularhypidiomorphic,withagrainsizebetween1and2mm(Figure 4B).Itsessentialmineralogicalcomponentsarequartz,plagioclase,alkalifeldspar,and biotite,althoughthelatterinasmallerproportion.Apatite,opaqueminerals,andzircon areaccessoryminerals.Chlorite,whichappearsbecauseofthealterationofbiotitecrys‐
Minerals2024,14,1948of16 tals,andsericite,duetothealterationofalkalifeldspars,aresecondaryminerals.Aninterestingtexturalcharacteristicofthesegranitesisamicrographictexturewithintergrowthsofquartzandalkalifeldspar,whichgivesrisetosingularblackandwhitepatternswhenviewedunderthepetrographicmicroscopewithcross‐polarizedtransmitted light.(Figure5B). Figure5.Granite.(A):CapstoneofgraniteinLaPastora(viewfrombelow).(B):Arepresentative thin‐sectionphotomicrographofthisstone.(C):OutcropofthegranitenearGuillena.(D):Athin sectionofgraniteinthelatteroutcrop. Asmentionedabove,granitecapstonenumber8(Figures2and6)partiallyincludes anaplitedykeononeofitsedges.Apliteisasubvolcanicrockwithacompositionsimilar togranitebutwithaveryfinegrainsizeandawhitishcolorduetotheabsenceofblack micas(biotites). Figure6.(A):Capstone8ofLaPastora.Itisagraniteblockwithanaplitedykeontherightandis ofalightercolor.(B):SamesituationinthefieldoutcropintheGuillenaarea. Calcareoussandstoneisthethirdrocktypefoundinthemonument(Figure7A)and istheonethathasbeenusedwithgreaterfunctionality,asmentionedabove(Figure2).
Minerals2024,14,1949of16 ThesearerocksoftheNeogeneagethatpresentnumeroussedimentaryandbiogenic structuresoriginaltothedeposit(synsedimentary)andpriortothediageneticprocesses ofconsolidationofthesedeposits.Amongthesedimentarystructures,thereareveryevidentcurrentmarksaswellaslaminations,mainlyhorizontal.Regardingthebioturbation structures,theOphiomorphaichnogenus,whichareverticalandhorizontalburrowsrelatedtotheactivityofdecapodcrustaceans,standoutfortheirabundance. Figure7.Calcareoussandstone.(A):CapstoneofthesandstoneinLaPastora(viewfrombelow). (B):Arepresentativethin‐sectionphotomicrographofthislithologyfromthemonument.(C):OutcropofcalcareoussandstoneoftransitionfaciesinCoriadelRío.(D):Athinsectionofthisrockis inthelatteroutcrop. Ontheotherhand,somesandstoneslabspresentbioerosionstructuresandremains ofrecentmarineorganisms,suchasostreids,barnacles,andpetrophagousbivalves,the latter(PetricolalithophagaRetzius)insidetheirboringexcavatedintherockitself(Figure 7A)[7,8]. Inthinsections,thecalcareoussandstonehasaveryfinegrainsize(around0.1mm) andisgenerallywellsorted(Figure7B).Mineralogically,itisessentiallycomposedof quartzgrainsinapercentageofaround60%,withangulartosubangularshapes,and abundantfossilremains(foraminifera,bivalves,spicules,andechinodermplates)inapercentageofaround20%.Minormineralcomponentsincludeplagioclase,whitemicas,tourmalines,andopaqueminerals.Therestoftherock(20%)iscarbonatecement. 5.2.PetrologicRelationshipsbetweentheStonesoftheTholosandNearbyOutcrops LaPastoratholosislocatedonasubstrateofsoftsediments,specificallyonyellow sandysiltswithcalcareousnodulesfromtheLowerPlioceneoftheGuadalquivirBasin (Figure3).Therefore,thestonematerialsusedinitsconstructionwerequarriedfromareas notinitsimmediatesurroundings.Inordertofulfillthemainobjectiveofthisstudy,once thematerialsofthemonumenthavebeencharacterizedandclassified,thenextstepisthe analysisofthenearestoutcropsofsimilarrocks,accordingtothegeologicalframework seenabove.Inthisway,adetailedpetrographiccomparisonofthedifferentlithofacies usedfortheconstructionofthetholoswiththegeologicaloutcropscanthenbemade.
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