Animal abundance and redox conditions during the Furongian Cambrian SPICE event, western Utah

The Steptoean Positive Isotopic Carbon Excursion (SPICE) is recognized as a global perturbation of the carbon cycle, with δ¹³C excursions (+4–5‰) found worldwide. The SPICE occurred in the Furongian Epoch of the Cambrian Period (∼500 Ma) and is unique among Paleozoic positive Carbon Isotope Excursions (CIEs) for its magnitude and global correlation, and has been well studied, though its causative mechanism is still debated. The Lawson Cove and House Range sections of western Utah are two localities where the SPICE was first reported and are relatively fossiliferous and thick, allowing us to document shifts in skeletal abundance and diversity through point counts of thin sections coupled with δ¹³C_carb, δ¹³C_org, TOC, and Hg measurements through both sections. The concurrent brief disappearance of trilobites at the onset of the SPICE in both sections, aligned with the Marjumiid-Pterocephaliid biomere boundary, supports a shared mechanism for the δ¹³C spike and the extinction event. The greatest abundance of fossils was found during the rising limb of the SPICE, reaching, or exceeding 49% of points per slide in both sections. The highest SPICE δ¹³C values correlated with a brief absence of fossil material in the Lawson Cove section. The House Range recorded a prolonged depauperate stretch during the peak δ¹³C values of the SPICE, correlated with a facies change at the transition into the Johns Wash Limestone Member of the Orr Formation. The differences seen between the sections highlight the impact of local processes in recording the SPICE event.