The Lower Ordovician (Tremadocian to Floian) graptolite fauna of Hunneberg, Västergötland, Sweden

Overview & Synopsis

The Diabasbrottet section at Hunneberg, Västergötland, Sweden is the type section (GSSP) for the Floian Stage, the second stage of the Ordovician System. The base of the Floian is determined by the First Appearance Datum (FAD) of the graptolite species Paratetragraptus approximatus, appearing at the same level as the typically Scandinavian Tetragraptus phyllograptoides, allowing the level to be determined also where the index species is lacking. The section is correlated worldwide through the presence of its graptolite faunas, but also through the presence of conodonts of the Paroistodus proteus conodont zone. Research in the graptolite faunas of Hunneberg and surrounds began in the late 19th and early 20th century, but a detailed taxonomic treatment has not been undertaken hitherto. This is despite the biostratigraphic ranges of the main faunal elements being well known and used for the definition of the Diabasbrottet section as the Global Stratopype Section and Point (GSSP) for the Floian. The revision of the faunas documents the most complete and highly diverse graptolite faunas from the late Tremadocian to early Floian known worldwide and also indicates a considerable biogeographical faunal differentiation in this time interval. The faunal composition indicates higher latitude faunas with a number of cold-water endemic faunal elements. New species are Jishougraptus hunnebergensis n. sp., Tetragraptus gerhardi n. sp., Baltograptus novus n. sp., Baltograptus floianus n. sp., and Cymatograptus kristinae n. sp.