The Lawsonian Stage - the Eoconodontus notchpeakensis FAD and HERB carbon isotope excursion define a globally correlatable terminal Cambrian stage

Bulletin of geosciences

Westrop SR¹  Adrain JM¹  Landing E¹ 

关键词: Cambrian;    Lawsonian Stage;    Utah;    United States;    conodonts;    agnostoids;    HERB excursion;   

DOI  :  

来源: Czech Geological Survey

【 摘 要 】

ThebestdefinitionforthebaseoftheterminalCambrian(Stage10)istheconodontEoconodontusnotchpeakensisFAD±onsetoftheHERBcarbonisotopeexcursion.Thesehorizonsallowpreciseintercontinentalcorrelationsindeepmarinetoperitidalfacies.TheagnostoidLotagnostusamericanus(Billings,1860)FADhasbeensuggestedasaStage10base,butrestudyoftypesandtypotypesshowsthatthespeciesoccursonlyinLateCambrian(Sunwaptan)debrisflowbouldersinQuebec(Westropetal.,thisvolume).Non-Quebecreportsof"L.americanus"areanamalgumofsmallsamplesofoftenpoorlydocumentedspecimenswitheffaced–highlyfurrowedcephalaandpygidiaandwithorwithoutahighlytrisectedpygidialposteroaxis.Manyoftheseoccurrenceshavelocalspeciesnames,butnoevidencesuggeststhattheyrecordintraspecificvariationofagloballydistributedtaxon.TheyarenotsynonymsofL.americanus.Lotagnostus,largelyadysoxicform,doesnotallowprecisecorrelationintooxygenatedplatformfacies.AnotherproposalusedtheconodontCordylodusandresiFADasaStage10base,butotherworkshowsthisFADisdiachronous.AnunrealisticapproachtoL.americanus’systematicsandthecorrelationuncertaintyofC.andresiareovercomebydefiningaStage10baseatthegloballyrecognizableE.notchpeakensisFAD,withtheC.andresiFADausefulproxyoncool-watercontinents.The"LawsonianStage",namedforLawsonCoveinwesternUtah,hasabasalGSSPattheE.notchpeakensisFADandreplacesinformalStage10.TheLawsonian,~150m-thickinwesternUtah,underliesthebasalOrdovicianIapetognathusZone.

【 授权许可】

Unknown