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Publication Date

2022-05-09

First Advisor

Sara B. Pruss

Document Type

Honors Project

Degree Name

Bachelor of Arts

Department

Geosciences

Keywords

Steptoean, Orr formation, Mercury, House range, Carbon isotopes

Abstract

The Steptoean Positive Isotopic Carbon Excursion (SPICE) is recognized as a global perturbation of the carbon cycle, as sections with excursions in δ13C (+4-5‰) have been found worldwide. The SPICE occurred in the Furongian Cambrian (~500 Ma) and is unique among Paleozoic positive Carbon Isotope Excursions (CIEs) for its length, spanning ~4 million years, and its occurrence in a period with no known glaciation. The SPICE is well studied, though its mechanism is still unknown and debated. The event is constrained within biostratigrahic units, with the onset aligned with the Marjumiid-Pterocephaliid biomere boundary and its falling limb overlain by the Pterocephaliid-Ptychaspid biomere boundary. However, these correlations are not recorded to cooccur in every SPICE section, highlighting the impacts of local processes on recording a global signal. Recent work has interpreted mercury enrichments accompanying the SPICE in Scotland and Newfoundland as proxy evidence for local redox oscillations. The Lawson Cove and House Range sections of western Utah are two of the localities where the SPICE event was first reported. Compared to typical SPICE sections, these are relatively fossiliferous and thick, allowing us to observe shifts in skeletal abundance at a high resolution as well as geochemical analyses of proxy environmental data. To investigate changes in faunal abundance and diversity throughout the SPICE interval we quantified fossil material abundance and diversity through point count analyses of thin sections along with presence absence surveys. Fossil diversity was found to be high during the rising limb of the SPICE in both sections, with a noticeable absence at the onset of the event. The House Range recorded a prolonged depauperate stretch during the peak values of the SPICE, during facies change at the transition into the Johns Wash Limestone Member of the Orr Formation. The differences we see between the sections highlight the impact of local processes in records of the SPICE event.

Rights

©2022 Amelia E. Olsen. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.

Language

English

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