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TitreThe Carnian-Norian boundary in Haida Gwaii: preliminary observations on the conodont faunas and their calibration with radiolarians
AuteurOrchard, M J; Carter, E S
SourceNew developments on Triassic integrated stratigraphy, Program and Abstracts; par Di Stephano, P (éd.); Balini, M (éd.); 2010 p. 40-41
Séries alt.Secteur des sciences de la Terre, Contribution externe 20100150
RéunionNew Developments on Triassic Integrated Stratigraphy; Palermo, Sicily; IT; Septembre 12-16, 2010
SNRC103B; 103C/16; 103F; 103G/13; 103J/04; 103K/01; 103K/02; 103K/03
Lat/Long OENS-133.5000 -131.0000 54.2500 52.0000
SujetsTrias supérieur; Carnien; Norien; distribution de la faune; assemblages fauniques; distribution de fossiles; fossiles; assemblages fossiles; paléontologie; Mésozoïque; Trias
ProgrammeGisements polymétalliques - nord-ouest de la Cordillère canadienne (Yukon et Colombie-Britannique), GEM : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
Conodonts and radiolarians co-occur in the Late Triassic Kunga Group of Haida Gwaii (formerly Queen Charlotte Islands), part of the allochthonous Wrangel terrane that was accreted to western North America subsequent to its formation in more southerly latitudes. Revision of the Carnian-Norian boundary (CNB) conodont succession in the Pardonet Formation of northeast British Columbia (NE BC) prompted a reappraisal of the Kunga conodont faunas, which have elements in common with those from both the former region and with Eurasian Tethys. For example, many important CNB elements of the primitius and parvus-echinatus groups are common to both the Kunga Group and Pardonet Formation, whereas some other taxa such as the Tethyan Neocavitella occur only in Haida Gwaii.
Several sections on Haida Gwaii contribute valuable information on the association of conodonts and radiolarians around the CNB. Chief amongst these are Sadler Point, Frederick Island, Shields Bay, Huxley Island, Kunga Island, and Kunghit Island. In particular, at Sadler Point a succession that begins low in the Upper Carnian (Dilleri ammonoid Zone) ranges up through the Lower Norian Epigondolella quadrata Zone and embraces the CNB, which can be recognized by both the succession of conodonts and by the conodont faunal turnover recognized in the Pardonet Formation (Orchard, 2007, fig. 5). Many of the morphospecies newly differentiated in NE BC are recognized in the Kunga Group, as are the intervals characterized by the samueli, 'pseudoechinatus', primitius, orchardi, and quadrata indices.
Amongst radiolarian species, the boundary interval is marked by the incoming at several levels of new species, most of which generally have been considered as either uppermost Carnian/lowermost Norian or lower Norian in the past (Blome, 1984; Tekin, 1999; Carter & Orchard, 2000; Bragin, 2007). Detailed sampling at Sadler Point produced two successive radiolarian faunas separated by about 3 m. The older one is characterized by Braginastrum curvatus Tekin, Catoma geometrica Blome, Icrioma deweveri (Tekin), I. tetrancistrum De Wever, Kahlerosphaera kermerensis adentta Tekin, Bulbocyrtium insolitum Blome group, Mostlericyrtium sitepesiformis Tekin, Pachus longinqus Blome, Spinosiocapsa? yazgani Tekin, Trilatus praerobustus Sugiyama and Xipha nodosa Sugiyama. Some of these taxa can be shown to occur earlier elsewhere on Haida Gwaii (e.g. Kunga Island, Shields Island), but their upper range is not yet established. Associated conodonts generally indicate a latest Carnian age.
The younger radiolarian fauna appears concurrently with the distinctive Metapolygnathus parvus group conodont fauna at Sadler Point and also on Frederick Island; also present in these collections are the conodonts 'Epigondolella' orchardi and Norigondolella sp. Notable among the radiolarians are Capnodoce crystallina Pessagno, Icrioma cruciformis Tekin, Loffa mulleri Pessagno, Paleosaturnalis izeensis Blome, Corum carinatus (Tekin), Hetalum parvis (Tekin) and Veghia sulovensis Kozur & Mock. Together, these two succeeding faunal levels indicate that the transition from a typically Upper Carnian to Lower Norian radiolarian fauna takes place over a very short distance. Comparison with radiolarians reported from Pizzo Mondello (Nicora et al., 2007) suggests that this CNB succession of radiolarians in Haida Gwaii is probably older than the Norian fauna from Pizzo Mondello.