Abstract
Twenty-five species of trilobites are described, some in open nomenclature. They represent four faunules of Dresbachian age and one faunule of possibie pre-Dresbachian age from the lower 150 m of the Cass Fjord Formation in Daugaard-Jensen Land, western North Greenland. The Cass Fjord Formation ranges in age from Middle Cambrian-Early Ordovician, although until recently it was widely assumed to be entirely of Ordovician age. All the trilobites are typical North American endemic forms. New taxa include: Bonneterrina greenlandica n. sp., Prolonchocephalus spinosus n. gen. n. sp., Kingstonia peltate n.sp., and Terranovella arcuata n. sp. Biogeographic affinities of the older faunules are with faunas of the inner part of the carbonate belt of the Cordilleran region, while the younger faunules have affinities with faunas from the outer(?) part of the carbonate belt in the northern Appalachian region. Evidence of extension of the Dresbachian-Franconian cratonic unconformity to western North Greenland is presented and the problem of repetition of trilobites in the crisis fauna at the base of the Pterocephaliid biomere is discussed.
Highlights
It is characterised by small trilobites with an unfurrowed, inflated or anteriorly expanded glabella, small palpebrallobes situated anterior to the glabellar midlength, and no clearly defined frontal area
This genus has been characterised by relatively generalised ptychoparioid trilobites with an evenly defined, anteriorly tapered glabella strongly rounded at the front, palpebrallobes opposite or slightly posterior to the glabellar midlength, and slightly cedariform posterior limbs
The cedariform nature is confirmed for B. prima Lochman, B. appalachia and B. greenlandica n.sp. by the associated free cheeks which show the posterior section of the facial suture crossing the lateral border furrow of the cheek before curving backward to the cephalic margin
Summary
The idea of a concentric development of facies-controlled trilobite faunas around North America during Cambrian time was first stated by Lochman-Balk & Wilson (1958) and later elaborated by Palmer (1972, 1974). A number of Middle and Late Cambrian faunas were collected and submitted to Palmer who identified Dresbachian and Trempealeauan faunules from localities within the Cass Fjord Formation. The lowest third of the formation is dominated by the greenish grey, nodular and 1enticular, lime muds and intraformational conglomerates considered characteristic of the formation as a whole It contains two conspicuous resistant mapping horizons (figs 5,6) yielding the faunas described members B and D of present usage, which were rather inappropriately termed the 'lower and upper massive' units by Henriksen & Peel (1976). Reasonable interpretation of these differences may become more apparent as our understanding of the palaeogeography of the Cambrian regarding ocean-current circulation and elimate zonation improves
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