CAMBRIAN ECHINODERMS, BRACHIOPODS AND SILICIFIED MICROFOSSILS FROM THE PEERLESS FORMATION, COLORADO

The Peerless Formation of Colorado has been assigned to the Euconodontus Zone of the Upper Cambrian. This formation has also yielded characteristic Upper Cambrian trilobites. We report here new occurrences of Cambrian echinoderms, brachiopods and silicified microfossils from the Peerless Formation. Specimens occur in float blocks of a poorly exposed Peerless Formation locality on the Ute Trail south of Aspen. The echinoderm specimen consists of a primitive echinoderm column, and appears to be either a rhombiferan cystoid or an eocrinoid column. This is the first echinoderm fossil reported from the Peerless Formation, and represents an important find if it extends the range of rhombiferan cystoids back to the Upper Cambrian. The brachiopod fossils consist of well preserved valves of probable syntrophiid brachiopods. The specimens have curious v-shaped cardinalia not resembling those known from other syntrophiidinid genera. The brachiopods are associated with thickly lined burrows up to 6 mm in diameter. Microbial Girvanella filaments occur in chert nodules in reddish, impure Peerless Formation carbonate. The Girvanella is opalized and most easily viewed in thin section under crossed polars. This represents an unusual microfossil occurrence, as silicified microbial filaments, common in Precambrian cherts, are comparatively rare in Cambrian sediments. The Peerless Formation represents a transgressive rock unit that is nevertheless separated from the overlying Manitou Formation by a significant hiatus. Continuing study of the sedimentology of the Peerless Formation will help to describe the unusual depositional environment of this new fossil assemblage.