Geological implications of Late Cambrian trilobites from the Collier Shale, Jessieville area, Arkansas

Abstract

Late Cambrian shelf trilobites characteristic of the Elvinia and Taenicephalus Zones (Franconian Stage) have been recovered from seven localities in newly recognized outcrops of the Collier Shale near Jessieville, Arkansas. Deposition of the Collier Shale spanned the Cambrian-Ordovician boundary; Late Cambrian trilobites occur in the lower part and Early Ordovician conodonts occur in the upper part of the formation. The trilobites are well known from many shallow-water shelf localities in North America, and their presence indicates that the Benton uplift is not an exotic terrane but an original part of North America. The thin, dark limestones containing the trilobites were deposited in a deep-water, outer-shelf or continental-slope location, and they establish an approximate position for the Late Cambrian shelf edge along the southern margin of North America.