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