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TitreMultiple conodont lineages across the Carnian-Norian boundary in North America: new taxonomy and biochronology
AuteurOrchard, M J
SourceProceedings of the 21st Canadian Paleontology Conference; par Haggart, J M (éd.); Smith, P L (éd.); Canadian Paleontology Conference Proceedings no. 9, 2011 p. 40-41
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120092
Réunion21st Canadian Paleontology Conference; Vancouver; CA; août 19-22, 2011
Documentpublication en série
Lat/Long OENS-123.0000 -122.5000 58.2500 58.0000
SujetsCarnien; Norien; fossiles; biostratigraphie; taxonomie; stratigraphie paléontologique; Trias supérieur; isotopes de carbone; Ammonoidée; paléontologie; stratigraphie
Programmebassins sédimentaires du Yukon, GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
At Black Bear Ridge on the perimeter of Williston Lake in northeast British Columbia, a prospective GSSP for the Upper Triassic Carnian-Norian boundary (CNB), continuously outcropping strata have yielded important ammonoids, bivalves, a carbon isotope anomaly, and a remarkable succession of abundant and diverse conodont faunas, many of which are new. Nine conodont faunas are differentiated within an interval that broadly encompasses the Macrolobatus and Kerri ammonoid zones. These include conodont zones named for samueli, primitius, orchardi, and quadrata, as well as currently unnamed intervals. Within a few metres of strata (Faunas 6-8 of Orchard, 2010), identified as embracing the preferred CNB, multiple conodont event datums are recognized. These are mostly linked to rapid and progressive morphogenesis in reconstructed lineages prior to a major faunal turnover. These events include: FAD of Gen nov. A sp. nov. A + Gen nov. C sp. nov. A; FAD of 'Epigondolella' orchardi; FAD of Metapolygnathus parvus s.s.; FAD of M. ex gr. parvus-echinatus + FAD of Gen nov. B sp. nov. A; LAD of multiple unornamented ¿metapolygnathids;¿ and FAD of common Norigondolella. The tentatively named parvus-echinatus group appears to represent the evolutionary end members of several lineages of 'metapolygnathids': they are relatively small elements characterized by strongly reduced platforms, long blades, and pits located beneath the junction of the two. Gen nov. A and B are ornate elements formerly regarded as variants of Epigondolella primitius Mosher and subsequently assigned to Metapolygnathus on the basis of their anteriorly situated pit. They are characterized by, respectively, pointed and markedly asymmetric platforms. Elements with generally rectangular platforms (including primitius and orchardi) are also assigned to a new genus. Within all of these, as well as those with strongly reduced platforms ('Orchardella?'), successions of species show progressive development of discrete and sharp anterior nodes, carina variation, and anterior migration of the pit. The genus Epigondolella is retained for E. quadrata and younger Norian species, whereas Carniepigondolella is restricted to older Carnian forms. Newly recognized and reclassified conodont taxa within a phyletic framework provide multiple indices for a refined biochronology and for boundary definition or proxy.