Distinctive changes in carbon isotope curves are used extensively alongside trilobite faunal turnover in the international correlation of Cambrian strata. One such isotopic signature, called “SPICE” (Steptoean Positive Isotope Carbon Excursion), is widely used, but in North America, the co-occurring trilobite fossils have never been illustrated. We here describe, discuss, and illustrate the 34 trilobite species (two new) that occur below, within, and above the SPICE from the same section where the carbon isotope data were collected in Utah. The illustration of the specimens, rather than just listing taxa, allows other scientists to evaluate the conclusions made here: the SPICE began in the Aphelaspis Biochron and ended within the Elvinia Biochron.
The trilobite faunas that occur with the Steptoean Positive Isotope Carbon Excursion (SPICE) at Smithfield Canyon, Utah, have been reported, but not illustrated. Given the importance of the SPICE at this section for international correlations, the trilobites from new collections from the upper Nounan Dolomite to lower St. Charles Formation at Smithfield Canyon are reported herein and integrated with the previously reported taxa. Trilobite assemblages indicate that the upper Cedaria to the Ellipsocephaloides biozones (Miaolingian Series, Guzhangian Stage to Furongian Series, Jiangshanian Stage) are present stratigraphically below or above the SPICE.
Some of the taxa reported herein may represent new species, but they are not represented by well-enough preserved specimens and are left in open nomenclature. However, Kingstonia smithfieldensis n. sp. and Bromella utahensis n. sp. are named on the basis of common and well-preserved specimens.
New carbon isotope data from Smithfield Canyon from an overlapping section of the lower St. Charles Formation, that add to the overall shape of the SPICE curve, are presented. The new δ13C values above the Elvinia Biozone range from –0.36‰ to +1.5‰, confirming that the SPICE concludes within the Elvinia Biozone.
