CAMBRIAN (STEPTOEAN-BASAL SUNWAPTAN) TRILOBITE BIOSTRATIGRAPHY OF THE HONEY CREEK FORMATION, WICHITA MOUNTAINS, OKLAHOMA

The sandy carbonates of the Honey Creek Formation are well exposed in a section at Ring Top Mountain on the north flank of the Wichita Mountains. Abundant trilobites offer an opportunity to revise the biostratigraphy of the Steptoean-Sunwaptan boundary interval. A succession of assemblages through the Steptoean support previous suggestions that this part of the formation can be divided into at least two distinct zones. Camaraspis parabola Frederickson is a short ranging species that occurs in the lower part of the formation in association with species of Kindbladia, Apachia and Xenocheilos. These species are absent from younger faunas dominated by Camaraspis convexa (Whitfield). The base of the Sunwaptan is marked by the appearance of species of Comanchia, Dellea and Sulcocephalus, and the extinction of most genera from the underlying fauna. This basal Sunwaptan assemblage, usually assigned to the Irvingella major Zone, persists through a surprisingly thick interval of about two meters of section. Well-preserved sclerites of Irvingella occur abundantly in a succession of bioclastic rudstones. They record the presence of several distinct morphotypes whose relationship to I. major Ulrich and Resser, a widely reported species based on sandstone internal molds from the Upper Mississippi Valley, is unclear. The data do cast doubt on the notion of a single, geographically-widespread species of Irvingella at the base of the Sunwaptan. Rather, “Irvingella major” likely represents a plexus of closely related species with a far more complex geographic and environmental distribution pattern.