| Description |
The Middle Cambrian Wheeler Formation in the Drum Mountains represents the transition between open-shelf and "deeper water", off-shelf environments. Lithologic evidence suggests frequent oscillation of depositional environments, which has resulted in three recognizable facies: The Shallow subtidal facies which is dominated by non0agnostid trilobite biosparites, oosparites, and oncolite-bearing intrasparites. The Open shelf facies which is characterized by mottled pelsparites, biomicrites or biosparites with patchy occurrences of micrite, and articulated trilobites. The "Deeper water" facies which consists of dark, even planar, 1_to 6-inch thick limestone beds interbedded with thin, fissile carbonate claystones; agnostid trilobites and sponge spicules make up the fauna. Faunal assemblages further support the interpretation of a transition between open shelf and"deeper water." The shallow subtidal facies is dominated by assemblages of diverse, probably benthic, non-agnostied trilobites; these are usually disarticulated and found in a sparry cement. The open shelf facies is characterized by sparse occurrences of fully articulated, non-agnostid specimens, and (or) bioturbated pelsparites containing non-agnostid fragments. The "deeper water" facies contains generally sparse, pelagic, agnostid trilobites. From the fossils that were collected, 24 species of non-agnostid trilobites are described or discussed. These belong to the lower Bolaspidella Assemblage Zobne. The following seven species are new: Elrathia granulosa, elrathia eardleyi, Modocia convexa, olenoides trispinus, Semisphaerocephalus voraginosus, Spencella drumensis, and Zacanthoides wheeleri. |
