Trilobites of the Upper Cambrian (Marjuman) Pika formation of the Southern Canadian Rocky Mountains

摘要

The Upper Cambrian Pika Formation in the southern Canadian Rocky Mountains forms acomplete lithologic Grand Cycle. The overall pattern of deposition is one of shallowingupwards from a subtidal, muddy, storm-influenced basin to a shallow carbonate bank. ThePika passes gradationally into the overlying inter- to supratidal siliciclastics of the ArctomysFormation. This transition probably reflects a fall in relative sea level.2Twenty seven collections from three sections yielded trilobites. The faunas are assigned totwo low-diversity biofacies: the Marjumia - Spencella Biofacies and the GZyphaspis -menomoniid Biofacies. In contrast to biofacies of deeper, open-shelf environments, such asthe Wheeler and Marjum formations of Utah, the Pika biofacies lack agnostid trilobites.Consequently, agnostid-based zonations defined elsewhere in North America cannot be appliedto the Pika and a new sequence of three zones and one informal fauna is proposed for use ininner shelf facies.Eleven species belonging to six genera are described and illustrated. The species Marjumiabagginsi is new. Other genera present are: Bolaspidella, Knechtelia, GZyphaspis andSpencella, in addition to a number of indeterminate forms