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TitreThe Carnian/Norian boundary succession at Berlin-Ichthyosaur State Park (Upper Triassic, central Nevada, USA)
AuteurBalini, M; Jenks, J F; Martin, R; McRoberts, C A; Orchard, M J; Silberling, N J
SourcePaläontologische Zeitschrift vol. 89, issue 3, 2014 p. 399-433,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20140177
Documentpublication en série
Mediaen ligne; numérique
Lat/Long OENS-118.5000 -117.2500 39.5000 38.7500
SujetsCarnien; Norien; biostratigraphie; taxonomie; assemblages fossiles; fossiles; distribution de fossiles; corrélations stratigraphiques; corrélation; paléontologie; stratigraphie; Mésozoïque; Trias
Illustrationslocation maps; stratigraphic columns; photographs
ProgrammeBassin de Sverdrup de l'ouest de l'Arctique, GEM2 : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
The Upper Carnian-Lower Norian (Upper Triassic) Luning Formation at Berlin-Ichthyosaur State Park (BISP) in central NV (USA) has been sampled using for the first time the bed-by-bed approach for ammonoids, pelagic bivalves, and conodonts, more than 60 years after its first description by Silberling (U.S. Geological Survey Professional Paper 322: 1-63, 1959). BISP is historically important for the definition of the uppermost Carnian of the North American Triassic chronostratigraphic scale and is known worldwide as one of the most important ichthyosaur Fossil-Lagerstätte because of its extraordinary record of 37 articulated, large-sized specimens of Shonisaurus popularis. Nearly 190 ammonoids were collected from two stratigraphic sections, documenting all the latest Carnian to Early Norian ammonoid faunas previously described by Silberling. Halobiids were collected from five levels, and the first report of conodonts from BISP includes faunas from 13 levels. The ~340-m thick Brick Pile section, the most complete in the study area, includes the uppermost Carnian Macrolobatus Zone, which provides conodont faunas of the lower primitia zone and Halobia septentrionalis. The 200-m thick lowermost Norian Kerri Zone, which begins 52 m above the Macrolobatus Zone, yields conodonts of the upper primitia zone in its lower part, together with H. cf. beyrichi and H. cf. selwyni. The ichthyosaur-bearing interval, whose stratigraphic position has been interpreted quite differently by previous authors, is documented in the uppermost Carnian Macrolobatus Zone and is characterized by rich Tropites-dominated ammonoid faunas and by the onset of Halobia. All models proposed by various workers to explain the unusual ichthyosaur record are discussed and an additional explanation for the main ichthyosaur-bearing bed is proposed. The new hypothesis is that a harmful algal bloom (HAB) may have been the trigger for the mass mortality recorded in this level. Although the C/N boundary in the Brick Pile section lies within a 52 m interval that presently lacks paleontologic data, this succession is included in a small group of sections that are expected to contribute to the definition of the GSSP of the Norian stage. Correlation of the Brick Pile section with the best Carnian/Norian sections in northeastern British Columbia is discussed. Compared to the British Columbia Juvavites Cove and the GSSP candidate Black Bear Ridge sections, the Brick Pile section exhibits an ammonoid and Halobia record that is slightly more similar to that of the Tethyan sections. Correlation of the Brick Pile section with the second GSSP candidate Pizzo Mondello (Sicily, Italy) well demonstrates the significant problems encountered in calibration of the Tethyan and North American scales.
Résumé(Résumé en langage clair et simple, non publié)
Une étude portant sur la formation Luning du Trias supérieur, dans le parc d'État Berlin Ichthyosaur, au Nevada, a été entreprise par une équipe internationale de paléontologues en vue de contribuer à l'élaboration de l'échelle de temps internationale. Des ammonoïdés, des bivalves et des conodontes sont présents dans une section ayant produit des spécimens d'ichthyosaures articulés connus dans le monde entier. L'association de différentes espèces fossiles sert de norme de comparaison pour établir la limite entre les étages Carnien et Norien du Trias, et aide grandement à établir des corrélations à l'échelle mondiale entre des sections de référence en Colombie-Britannique et en Sicile.