New information on olenelline trilobites from the Cambrian Sekwi Formation in northwestern Canada

Abstract

A new species of olenelline trilobite, Nevadella keelensis, is described from the Early Cambrian (Cambrian Series 2, Stage 3) in the Sekwi Formation, Mackenzie Mountains, Canada. The difficulty in discerning between Nevadia Walcott, 1910 and Nevadella Raw, 1936 is discussed, and a revision of the two genera is suggested, particularly with the addition of Nevadella keelensis n. sp. A holmiid trilobite, perhaps conspecific with Esmeraldina rowei (Walcott, 1910), was also confirmed from the same locality. The E. sp. aff. rowei represents the narrow form of a species known for great variability in cephalic form. The trilobite material comes from a low diversity, shallow water, peritidal facies that was not sampled in previous studies of Cambrian fossils in the area, and could prove useful in facilitating biostratigraphic correlation across the Selwyn Basin and with other parts of Laurentia as well.Résumé : Une nouvelle espèce de trilobites olénellinés, Nevadella keelensis, du Cambrien précoce (série cambrienne 2, étage 3) de la Formation de Sekwi, dans les monts Mackenzie (Canada), est décrite. La difficulté de distinguer Nevadia Walcott, 1910, de Nevadella Raw, 1936, est abordée, et il est suggéré de revoir les deux genres, notamment avec l'ajout de Nevadella keelensis n. sp. Un trilobite holmiidé de cette localité, possiblement conspécifique d'Esmeraldina rowei (Walcott, 1910), a également été confirmé. Le spécimen E. sp. aff. rowei représente la forme étroite d'une espèce connue pour sa grande variabilité de morphologie céphalique. Les restes de trilobites proviennent d'un faciès péritidal d'eau peu profonde et de faible diversité que les études précédentes de fossiles cambriens dans la région n'avaient pas échantillonné. Ce matériel pourrait faciliter la corrélation biostratigraphique dans le bassin de Selwyn et avec d'autres parties du Bouclier laurentien.[Traduit par la Rédaction]

Phylogenetic response of naraoiid arthropods to early–middle Cambrian environmental change

“…Olenellids commonly inhabited tidal flat to middle shelf environments (Hollingsworth 2006; Abe et al . 2010; Foster 2011; Mángano et al . 2013; Paterson 2014; Fagetter et al .…”

New olenelloid trilobites from the Northwest Territories, Canada

“…The new material comes from the Sekwi Formation, Mackenzie Mountains, Northwest Territories, Canada. This formation has yielded a diverse array of early Cambrian trilobites (Fritz 1972;Abe et al 2010;Gapp et al 2011) as well as a well-preserved chancelloriid fauna (Randell et al 2005). The unit is relatively thick, consisting of 715 to 750 m of interbedded carbonate, shale, and sandstone, comprising mainly weathered limestone and dolostone, deposited during the Fallotaspis, Nevadella, and Olenellus trilobite zones (Fritz 1972(Fritz , 1973Randell et al 2005;Dilliard et al 2007Dilliard et al , 2010.…”

“…Casts were made of external moulds using latex for figuring (these are noted in figure descriptions). Sections given for the Sekwi Formation under "occurrences" refer to those used in Dilliard et al (2007), Abe et al (2010), and Gapp et al (2011).…”