简介：Diabasbrottet,selectedbytheInternationalSubcommissononOrdovicianStratigraphyandin2002ratifiedbytheInternationalCommissiononStratigraphyastheGSSPoftheSecond(Upper)StageoftheLowerOrdovician,islocatedontheHunnebergMountaininsouthwesternSweden.ThestratigraphicsuccessionrepresentsanoutershelfenvironmentneartheBalticShieldmargin.Theshale-dominated,biostratigraphicallycomplete,richlyfossiliferousboundaryintervaliscompletelyexposedinadisusedquarry.TheGSSPisinthelowerTФyenShale2.1mabovethetopoftheCambrianandismarkedbythefirstappearanceofthegraptoliteTetragraptusapproximatusNicholson.Theboundaryintervalcontainsadiversegraptolitefaunaandbiostratigraphicallydiagnosticconodontsandtrilobitesthatmakeitpossibletodefinetheboundaryintermsofzoneschemesbasedonthesegroups.Inthisrespect,theDiabasbrottetandnearbysectionsareuniqueintheworldamongdescribedlocalitieshavingthisboundaryinterval.BasedontheappearanceofT.approximatus,thebaseoftheSecondStagecanbeidentifiedinmanygraptolitiferoussuccessionsroundtheworldbutthisleveliscurrentlymoredifficulttorecognizepreciselyinsomecarbonatesequencesoutsideBaltoscandia.WeproposetheSecondStagebecalledtheFloanStage.ItisnamedfortheVillageofFlo,whichissituatedabout5kmsoutheastoftheGSSP.