Palaeoenvironmental and stratigraphic significance of Pliocene rhodolith beds and coralline algal bioconstructions from the Carboneras Basin (SE Spain)

[摘要] ThickrhodolithbedsoccurinthetransgressiveandhighstandsystemstractsoftheearlyPliocenesequenceintheCarbonerasBasininSESpain.Rhodolithbedsaccumulatedinmid-to-outerrampsettingsandintheleesideofaspitplatformduringthetransgressiveinterval,whereasrhodolithconcentrationsinthehighstanddepositsonlyformedinthemid-to-outerrampatthesouthernmarginofthebasin.Theelevationofrhodolithbedscomparedwithcoevalshoredepositssuggeststhatthebedsdevelopedatwaterdepthsofseveraltensofmetres(probablylessthan50m).Thispalaeodepthestimateisconsistentwiththecompositionofalgalassemblages,whicharedominatedbymelobesioidscommoninrelativelydeepplatformenvironmentsinthemodernMediterraneanSea.LithothamnionminervaeBasso,1995,L.philippiiFoslie,1909,andMesophyllumalternans(Foslie)Mendozaamp;Cabioch,1998withsubordinatePhymatolithoncalcareum(Pallas)Adeyamp;McKibbin,1970andM.macroblastum(Foslie)Adey,1970andlithophylloidsoftheLithophyllumincrustansPhilippi,1837-L.racemus(Lamarck)Foslie,1901complexarethemostcommonofatotalof21recordedspecies.Alltheidentifiedalgalspeciesarealsolivinginthepresent-dayMediterraneanexceptfortheextinctLithothamnionramosissimum(Reuss)Piller,1994andfortherecentSpongitesdecipiens(Foslie)Chamberlain,1993,whichhasbeenreportedintheIndo-PacificandSouthAdantic,butnotintheMediterranean.Moderateenergyandlowsedimentationratespromoteddevelopmentofrhodolithbedsinthetransgressivedeposits,buttheyarenotexclusivetothetransgressivesystemstractastheycontinuedtoaccumulateatthesouthernmarginduringthehighstand,beyondtheinfluxofsiliciclasticsthatreducedcarbonateproductionintherestofthebasin.Isolatedpillars(upto90cmhigh)orirregularpatches(upto2mhighand7mwide)ofcorallinealgal-bryozoan-bivalvebioconstructionsoccurinouterrampfine-grainedcalcarenites.Despitetheirsimilaritiestopillarsandlowreliefbuildupsconstructedbycorallinealgae(“coralligènedeplateau”)inthepresent-dayMediterraneanSea,thesebioconstructionsareuniqueasbryozoansarethemainbuildersandcorallinealgae(L.philippiiandM.lichenoides)playonlyasecondaryrole.IncontrastwithmodernMediterraneancorallinealgalbuildups,thelackofbioclasticdebrisderivedfromthebuild-upsinthesurroundingfine-grainedsedimentsandtheirgeneralmorphologysuggestthatthePliocenebioconstructionsintheCarbonerasBasindidnotcreatesignificantpositivereliefontheseafloor.

[学科分类] 生物科学（综合）

[关键词] Rhodolith beds;coralline bioconstructions;Pliocene;coralligène;Carboneras Basin;SE Spain;Couches à rhodolithes;constructions à algues corallines;Pliocène;coralligène;bassin de Carboneras;Espagne