Ostracods and rock facies across the Givetian/Frasnian boundary interval in the Sourd d’Ave section at Ave-et-Auffe (Dinant Synclinorium, Belgium)

Bulletin of geosciences

Petitclerc E¹  Devleeschouwer X¹  Maillet S¹  Preat A¹  Casier J-G¹ 

关键词: ostracods;    palaeoecology;    sedimentology;    Givetian/Frasnian boundary;    Fromelennes Formation;    Nismes Formation;    Dinant Synclinorium;    Ardenne;    Belgium;   

DOI  :  

来源: Czech Geological Survey

【 摘 要 】

OstracodsfromtheSourdd’AvesectionhavebeencollectedintheMoulinBoreuxandFortHulobietMembers(FromelennesFm.,GivetGroup)andinthePontd’AvignonMember(NismesFm.,FrasnesGroup).OstracodscollectedintheFromelennesFm.byMilhau(1983a)andintheNismesFm.byCasier(1987a)havebeenalsoreviewed.Forty-fourostracodspeciesareidentifiedintheFromelennesFm.and25intheNismesFm.TheybelongexclusivelytotheEifelianMega-Assemblage,andseveralassemblagesindicativeofrestrictedandshallowmarine,sometimesagitated,environmentsarerecognizedintheFromelennesFm.ThegreatrarityofostracodsintheupperpartofthisformationprovidesevidenceforlessfavourablelagoonalconditionsprobablyrelatedtoincreasingaridityattheendoftheGivetian.IntheFrasnesGroup,assemblagesareexclusivelyopenmarineandindicativeofincreasingwaterdepth.ThemajorityofostracodspeciesrecognizedintheGivetGrouparemissinginthebaseoftheFrasnesGroupasaconsequenceoftheFrasnesEvent.AsystematiclistofostracodsidentifiedintheFromelennesFm.atSourdd’Aveispublishedasanannex.SystematicsamplinghasbeencarriedoutinordertoestablishthesedimentologicalevolutionoftheenvironmentsandtodetailtheGivetian-Frasnian(G/F)transition.Thisallowedrecognitionof13microfaciestypesthatreplicatethestandardsequenceofPreatMamet(1989)fromopenmarineshallowsubtidaltorestrictedsupratidalnearemersion.TheBoreuxMemberandtheFortHulobietMemberdisplayrestrictedfacies(Amphipora,spongiostromidandalgalbafflestonesandbindstones,loferiteswithdesiccationlumps)withpoorlyfossiliferousbedsinterbeddedwithhigherenergypeloidalandsometimesooliticgrainstonefacies.Laminitehorizons,sometimeswithsmall-sizedlaterallinkedhemispheroidstromatolitesareuncommon,andareassociatedwithdolomicritesshowingpseudomorphsofevaporiteminerals.TheseevaporiticfaciesbecomecommonintheupperpartoftheFortHulobietMembersuggestingthepalaeoclimatebecamemorearidattheG/Ftransition.Metre-scalecyclicityispervasivethroughouttheGivetianpartofthesection.TheboundarybetweentheGivetGroupandtheFrasnesGroupisverydistinctiveinthefield,andischaracterizedbyatransitionfromrestrictedevaporativelagoonalfaciestoopenmarineinterbeddedmarlyshalesandnodularlimestones.TheupperpartoftheFortHulobietMemberconsistsofinterbeddedbiostromes(semi-restrictedstromatoporoidboundstones)followedbyAmphiporafloatstones,thenfossil-poorunitsandrestrictedsupratidallaminiteswithwell-developedfenestralfabrics.TheFrasnianPontd’AvignonMembercontainsarichfaunalassemblage(bryozoansbrachiopods,molluscs,nautiloids,tentaculitids)suggestinganabruptdrowningfromthemarginalGivetiancarbonateplatformintoaFrasniandistalrampordeepbasinalenvironmentbelowornearstormwavebase.

【 授权许可】

Unknown