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Sara B. Pruss
Bachelor of Arts
SPICE, Carbon isotopes, Mercury, Cambrian, Glauconite, Redox, Sauk
The Steptoean Positive Isotopic Carbon Excursion, or SPICE event, was a global +3-6‰ shift in d13C values during the later Cambrian (ca. 500Ma). The excursion has been broadly correlated with the Sauk II-III subsequence boundary in North America and several trilobite mass extinctions globally, yet the mechanism(s) for these events and the excursion itself are unconfirmed. The recent discovery of mercury enrichments accompanying the SPICE in Scotland has prompted reconsiderations about the global nature of the SPICE excursion and the use of mercury as a large igneous province (LIP) volcanism indicator. Sedimentary mercury enrichments have frequently been interpreted as a LIP indicator, yet modern studies have shown that mercury can be rereleased from sediments during anoxic intervals. To further investigate these new hypotheses, we analyzed mercury enrichments as well as a suite of other geochemical and mineralogical information in an outcrop of the SPICE located along the south-facing shore of the Port au Port Peninsula, western Newfoundland. These mixed carbonate and siliciclastic strata record small mercury enrichments coupled with high glauconite abundance after, but not during, the SPICE peak. Since glauconite is a mineral sensitive to local redox oscillations, we interpret the period just after the SPICE peak to have had frequent oxic/anoxic switches. The pattern of mercury enrichments found in Scotland, however, suggests redox oscillations constrained to the SPICE peak. These differences highlight how local processes can affect the manifestation of a global event in different environments. Both studies support the use of sedimentary mercury as a new proxy for tracking local redox oscillations.
©2021 Amy Patricia Isabelle Hagen.
Hagen, Amy Patricia Isabelle, "Evaluating redox conditions during the Cambrian SPICE event, western Newfoundland, Canada" (2021). Honors Project, Smith College, Northampton, MA.
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