Author: Karim, Talia S.

Source: Canadian Journal of Earth Sciences, Volume 45, Number 4, April 2008 , pp. 407-425(19)

Publisher: NRC Research Press

Abstract:

A single boulder (PH 8.14), recovered from unit 8 on the Point of Head, Cow Head Peninsula, Shallow Bay Formation (Cow Head Group), contains a unique olenid-dominated trilobite fauna composed of the following taxa: Boeckaspis geordii n. sp., Leiobienvillia terranovica (Rasetti, 1954), hystricurid n. gen. n. sp., Tulepyge sp. A, Tulepyge sp. B, Tulepyge? sp. C, and Symphysurina sp. The pelturine trilobite B. geordii dominates the assemblage. Boulder PH 8.14 consists of light grey-brown packstone to grainstone. This is atypical for olenid-dominated faunas, which usually occur in dark laminated limestones and shales. The fauna is likely earliest Ordovician in age, but a latest Cambrian age cannot be entirely ruled out. Regardless, this assemblage is unique in that it is the only known olenid-dominated fauna from Cambrian-Ordovicianboundary sediments in Laurentia. A phylogenetic analysis of Boeckaspis and other putatively closely related taxa (Westergaardia Raymond, 1924 and Jujuyaspis Kobayashi, 1936) was conducted. The results of the analysis indicate that Westergaardia is not monophyletic and as such it is considered a junior synonym of Boeckaspis herein.

Un bloc (PH 8,14) provenant de l'unité 8 de la Formation de Shallow Bay (Groupe de Cow Head), sur la Point of Head de la péninsule de Cow Head, contient une faune de trilobites singulière à prédominance d'olénides, composée des taxons suivants : Boeckaspis geordii n. sp., Leiobienvillia terranovica (Rasetti, 1954), hystricurid n. gen. n. sp., Tulepyge sp. A, Tulepyge sp. B, Tulepyge? sp. C et Symphysurina sp. Le trilobite pelturin B. geordii est l'espèce prédominante de l'assemblage. Le bloc PH 8,14, constitué de packstone à grainstone gris brun, est un hôte atypique de faunes à prédominance d'olénides, que l'on retrouve habituellement dans des calcaires et shales laminés de couleur foncée. Cette faune date probablement du début de l'Ordovicien, bien qu'un âge Cambrien terminal ne puisse être exclu. Quoi qu'il en soit, cet assemblage est unique en cela qu'il constitue la seule faune à prédominance d'olénides connue dans des roches sédimentaires de la limite Cambrien - Ordovicien de Laurentia. Les résultats d'une analyse phylogénétique de Boeckaspis et d'autres taxons de proche filiation putative (Westergaardia Raymond, 1924 et Jujuyaspis Kobayashi, 1936) indiquent que Westergaardia n'est pas monophylétique et est donc considéré dans le présent article comme représentant un synonyme junior de Boeckaspis.

Document Type: Research article

Publication date: 2008-04-01

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