Early Silurian brachiopods (]Rhynchonellata) from the S<:ElabonnFormation of the F�ingerikedistrict, Norway
ELSEBETH THOMSEN, JISUO JIN AND DAVID A. T.. HARPER
Thomsen, E., Jin, J. & Harper, 0.A.T. 2006--12-11: Early Silurian brachiopods (Rhynchonellata) from the SrelabonnF ormation of the Ringerike district, Norway. Bulletin of the Geological Society of Den mark, Vol. 53, pp. 111-126. © 2006 by Geological Society of Denmark. ISSN 0011---{;297. (www.2dgf.dk/ publikationer /bulletin).https ://doi.org/10.37570/bgsd-2006-53-06
A revision of Kirer'sindex fossils c,f "Etage" 6 in the Ringerike district of Norway reveals the pres ence of four species: Rostricellula wadti sp. nov., Platytroclialos ringerikensis sp. nov., Plati;trochalos rabbei sp. nov., and Zygospiraella duboisi. Rostricellula is a common Ordovician rhynchonellide brachiopod and is known to occur in the Lower Silurian as a holdover taxon in only a few localities worldwide. Previously, Platytrochal'osw as known only from the Lower Silurian (Uandoverian) rocks of Anticosti Island, easternCa nada. The occurrence of this rare genus in the Ringerike district pro vides additional information for the early evolution and palaeogeography of the taxonomically en igmatic family Leptocoeliidae. Zygospiraella is regarded as an index genus for the Rhuddanian, and the presence of Z. duboisi provides a useful biostratigraphic control on the age of the Srelabonn Formation.
Key words: Rhynchonellate brachiopods, Early Silurian, biostratigraphy,t axonomy, Norway.
Thomsen, E. [[email protected]], Department of Geology, Tromse University Museum, N0- 9037 Tromso, Norway; Jin, J. [email protected]], Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 587, Canada; Harper, D.A.T. [[email protected]), Geologisk Museum, 0ster Voldgade 5-7, DK-1350 J(gbenhavn I<, Denmark.
Despite their potential importance for the study of nides, and smooth athyridides, which are notoriously biotic recovery immediately after the Late Ordovi time-consuming for taxonomic examination. cian mass extinction event, Rhuddanian (earliest Sil Rhuddanian brachiopod faunas usually contain a urian) brachiopod faunas are generally poorly known lnixture of holdover taxa from the Late Ordovician compared to the large amount of data on the pre and newly evolved forms typical of the Early Silu extinction Ashgill, or post-extinction Aeronian and rian. Genera such as Mendacella, Eoplectodonta, Lep Telychian brachiopods worldwide. Early Llandovery taena, Eospirigerina, and Cryptothyrella are probably brachiopods from Wales (Temple 1970, 1987) are pre the most common brachiopods that survived the Late served mostly as moulds, making them difficult to Ordovician mass extinction event to become the com compare with the better preserved shelly material of mon brachiopods during the earliest Silurian. Some North America, Sibe1ia, Kazakhstan, and northern newly evolved forms (e.g. Viridita and Virgiana) may Urals (for a summary see Kovalevskii et al. 1991; Bez be widespread across several tectonic plates during nosova 1994). In North America, most Rhuddanian the Rhuddanian, whereas others are highly endelnic brachiopods remain to be studied systematically, taxa, among which is Platytrochalos dealt with in this except for those of the American lnid-continent (e.g. study, a genus known previously only from Anticos Amsden 1974) and the well-known Virgiana fauna ti Island. Qin et al. 1993, 1996). Some of the well-preserved During a Cand. scient. study (University of Co Rhuddanian brachiopod faunas from Anticosti Island penhagen), Thomsen (1981) described 31 brachiopod (eastern Canada), Manitoulin Island (Ontario, Cana species from Rhuddanian and Aeronian strata of the da), and the Illinois Basin (USA) are dominated by Ringerike district, including the index species of Kirer dalmanellid orthides, plectambonitoid strophome- (1908), i.e. Rostricellula n. sp. a, Rostricellula n. sp. b,
Thomsen et al.: Early Silurian brachiopods from the Scelabonn Formationof Ringerike district, Norway • 111