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TitreRadiolarians and conodonts across the Carnian-Norian Boundary in Haida Gwaii, British Columbia, Canada
AuteurCarter, E S; Orchard, M J
SourceProceedings of 13th INTERRAD, a conference on fossil and recent radiolarians; par InterRad; Radiolaria Newsletter vol. 28, 2012 p. 76-77
Séries alt.Secteur des sciences de la Terre, Contribution externe 20120103
RéunionInterrad 13, 13th Conference on Fossil and Recent Radiolarians; Cadiz; SP; mars 25-29, 2012
Documentpublication en série
SNRC103k/02; 103k/03
Lat/Long OENS-133.2500 -132.5000 54.2500 54.0000
Sujetsfossiles; Carnien; Norien; biostratigraphie; Radiolarie; Ammonoidée; paléontologie; stratigraphie; Trias
Programmebassins sédimentaires du Yukon, GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
The early Mesozoic radiolarian succession in Haida Gwaii is unrivalled in terms of both abundance, excellent preservation of the faunas, and because of their common co-occurrence with conodonts and macrofossils, which permit the intercalibration of fossil zonations. Radiolarians from stratigraphic sections at Sadler Point (uppermost Carnian to lower Norian) and Frederick Island (lower Norian) plus collections from selected localities included to better constrain the upper Carnian interval were studied to assess the character of faunas through the interval likely to embrace the as yet unde!ned Carnian-Norian Boundary (CNB). 'e faunas are diverse and contain over 130 species. These include species that are widely known in other areas of the world as well as many new undescribed species. The faunas compare most closely with those from central Oregon (Blome, 1984; Yeh, 1989) and Baja California (Pessagno et al.,1979), but many species described from Japan, Timor, the Philippines, the Northern Calcareous Alps and Tethys (i.e. Cypress, Greece, Sicily and Turkey) are common to abundant too. Many of the conodonts from Haida Gwaii are also known from Black Bear Ridge in northeastern B.C. (a proposed candidate GSSP for the CNB) and thereby permit recognition of conodont faunas differentiated by Orchard (2007, 2010). The pattern of radiolarian change across the CNB interval is characterized by the appearance of new species, there being very few extinctions. 'e oldest faunas co-occur with Carnian ammonoids of the Welleri Zone and conodonts originally assigned to the lower Metapolygnathus nodosus Zone (Orchard, 1991). This distinctive fauna occurs widely throughout Haida Gwaii and most of its species range upward across the CNB interval. The composition of younger radiolarian faunas changes gradually through the samueli to primitius conodont zones (equivalent to Faunas 1¿6 of Orchard 2010), which are broadly equivalent to the latest Carnian Macrolobatus ammonoid Zone. The FAD of Kahlerosphaera kermerensis adentata Tekin, a species formerly regarded as early Norian, occurs in the upper part of this interval. A major increase in diversity occurs around the beginning of Fauna 7 (of Orchard 2010), wherein the favoured CNB lies, with the ! rst appearance of over 34 radiolarian species including Corum speciosum Blome, Loffa mulleri Pessagno, Icrioma deweveri Tekin, Sarla curvatus (Tekin), Spinosicapsa? akayi (Tekin) and Veghia sulovensis Kozur & Mock. The FAD of a further 15 species, including Dumitricasphaera elegans Tekin, Hetalum parvus (Tekin), Kozuricyrtium carinatus (Tekin) and Pachus longinquus Blome occurs slightly higher in association with diminutive elements presently combined as the Metapolygnathus echinatus - M. parvus group. Together this ¿faunal bloom¿ marks the FAD of genera Catoma, Loffa,
Pachus and Renzium, and over half of the constituent species have been regarded as first appearing in the Norian. Further but lesser radiation occurs at higher stratigraphic levels.