Sedimentary mercury as a proxy for redox oscillations during the Cambrian SPICE event in western Newfoundland

Abstract

The Steptoean Positive Isotopic Carbon Excursion, or SPICE event, was a globally recorded +2‰ to +6‰ shift in δ13C values during the later Cambrian (ca. 500 Ma). The excursion is associated with regional sea level change and trilobite extinctions documented from multiple paleocontinents, yet the mechanism(s) for these events and the excursion itself are not fully understood. Recent studies have suggested that the SPICE is accompanied by global changes in redox conditions, which may have served as an extinction driver. Here, we present new geochemical and mineralogical data from an outcrop of the SPICE located along the Port au Port Peninsula in western Newfoundland. We focus on paired sedimentary mercury and glauconite enrichments as a potential redox indicator in an effort to evaluate local redox conditions during the SPICE in Newfoundland and assess the validity of Hg as a redox proxy. These strata record small mercury enrichments (<20 ppb) relative to SPICE background, sometimes coupled with elevated glauconite abundance. This coupling occurs after the carbon isotope peak, suggesting that the environment during the falling limb of SPICE experienced redox oscillations. Findings from this study supplement existing global proxies by adding information on redox conditions during the SPICE in a shallow shelf environment. Further, the coupling of Hg enrichments with elevated glauconite provides some support for the use of sedimentary Hg as a redox indicator when enrichments are elevated compared to background.