MAJOR AND TRACE ELEMENT ANALYSIS OF THE LATE CAMBRIAN SPICE EVENT FROM THE RHINEHART A-1 CORE, DALLAS COUNTY, IA

The late Cambrian Steptoean Positive Carbon Isotope Excursion (SPICE) represents a significant perturbation to the global carbon cycle in which carbonate carbon isotope values (δ¹³C_carb) undergo a 4-5‰ positive shift that is recorded in strata worldwide. Numerous studies interpret this event as an episode of enhanced organic carbon burial during an expansion of reducing conditions. Concurrent positive excursions in carbonate-associated sulfate and organic carbon isotopes coupled with a major extinction at the event onset further support this hypothesis as well as the global nature of the SPICE. Geochemical studies of the SPICE additionally present evidence of upheavals in trace metal cycling around the onset of the δ¹³C excursion, which provides critical insight into the interplay between changing marine redox conditions, nutrient cycling and availability, and extinction.

Here, we present a suite of high-resolution trace metal and rare earth element data from the SPICE in the Rhinehart A-1 core from central Iowa. The data reveal notable enrichments of these elements that are consistent with changing marine redox conditions and a substantial increase in primary production around the event onset, especially when considered with previously produced δ¹⁵N_bulk from this core. Both of these factors play a crucial role in deciphering the dominant control(s) and sequence of events responsible for driving such a large biogeochemical event. While these redox proxies cannot be applied to the global oceans, the relationships shown here between metal enrichment, nutrient cycling, deoxygenation of marine settings, and the onset of a widespread carbon cycle perturbation resemble those observed during other Phanerozoic biogeochemical events, ultimately serving as critical models when evaluating the biogeochemical signals preserved here as well as shedding more light on the evolution of the ocean-atmosphere-biosphere system.