The Diplacanthograptus caudatus Zone: a proposal for a new, globally recognizable, Upper Ordovician graptolite zone

• Daniel Goldman ^[1]
  1. [1] University of Dayton

     University of Dayton

     City of Dayton, Estados Unidos

     
• Localización: Serie correlación geológica, ISSN-e 1666-9479, ISSN 1514-4186, Vol. 17, Nº. 1, 2003
• Idioma: inglés
• Enlaces
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• Resumen

  • The Ordovician Sub–commission of the International Commission on Stratigraphy has recently redefined the base of the Upper Ordovician Series as the base of the Nemagraptus gracilis graptolite biozone. This designation recognized the tremendous utility of a globally identifiable biozone based on the first appearance of a cosmopolitan taxon that occurs within a consistent succession of other first appearance datums (FADs) (e.g., Finney and Bergström, 1986; Bergström et al., 2000). In the upper part of the range of N. gracilis, Climacograptus bicornis, members of the Orthograptus calcaratus species group, and a profusion of large dicellograptinids and dicranograptinids first appear (Finney and Bergström, 1986). This fauna is also widely known and can be precisely correlated across the world.

    Unfortunately, the correlation of post–Climacograptus bicornis Zone rocks is one of the long–standing problems in Ordovician graptolite biostratigraphy. Faunal provincialism has led to the construction of numerous separate zonations, 4 in North America alone. Establishing detailed correlations between these various zonations has proved difficult and often contentious (e.g., Riva, 1969, 1974; Berry 1970, 1977; Bergström, 1978; Finney, 1986). In this paper I will briefly review the post–Climacograptus bicornis Zone graptolite successions from several well known localities and suggest a more useful standardized zonation for this interval based on the Climacograptus – Diplacanthograptus lineages.