SKELETAL ABUNDANCE DURING THE CAMBRIAN SPICE EVENT, WESTERN UTAH

The Steptoean Positive Isotopic Carbon Excursion (SPICE) is a globally recorded positive shift (+4-5‰) in δ¹³C during the Furongian Epoch of the Cambrian. The SPICE event is recorded within thick, fossiliferous sections of the Orr Formation exposed at the Lawson Cove and House Range localities in western Utah. High resolution sampling through the SPICE event provided an opportunity to observe shifts in skeletal abundance and diversity through the excursion while tracking Hg abundances, total organic carbon, and organic carbon isotope ratios. In both sections, pre-SPICE intervals are characterized by low abundance of skeletal material, followed by a brief absence at the onset of the SPICE event. The rising limb of the SPICE has the greatest abundance of skeletal material observed in thin section with as much as 49% of skeletal material per slide in both sections. In the Lawson Cove section, the most positive δ¹³C values are aligned with a brief absence of skeletal material, while in the House Range, an extended absence of skeletal material overlaps with peak δ¹³C values. This prolonged depauperate stretch in the House Range is correlated with a marine regression recorded in the facies change from the Candland Shale Member into the Johns Wash Limestone Member of the Orr Formation. The geochemical and fossil differences between these two localities illustrate the impacts of local processes on the preservation of the SPICE event itself as well as its biological consequences.