Undergraduate Honors Theses

Thesis Defended

Spring 2018

Document Type

Thesis

Type of Thesis

Departmental Honors

Department

Geological Sciences

First Advisor

Alexis Templeton

Second Advisor

Jena Johnson

Third Advisor

Sebastian Kopf

Fourth Advisor

Amy Palmer

Abstract

The ancient ocean conditions and the mechanism(s) associated with the formation of the primary minerals of Banded Iron Formations (BIFs) have been debated overtime. Recent studies on BIFs have revealed trapped well-preserved nanoparticles of iron-silicates like Greenalite in chert nodules in BIFs (Rasmussen et al, 2015, 2016, 2017). This led to research into the chemical and biological conditions needed to produce an iron-silicate like Greenalite to help constrain ancient ocean conditions 2.5 Ga associated with the formation of BIFs. Initial experiments showed that forming abundant iron(II)-silicates similar to Greenalite required 1 mmol Fe2+ and 2.3 mmol silica in water at a pH ~8-8.3. Additional experiments were performed to test the effects iron-oxidation had on iron-silicate formation. Abiotically-produced iron-silicate precipitates were oxidized in the presence of an Fe-photoferrotroph, Rhodopseudomonas palustris (R. pal), over time. The presence of R.pal showed a transition from an iron(II)-silicate to an iron(II-III) intermediate to an iron(III) oxide over time using iron X-ray absorption spectroscopy (XAS) to assess the iron geochemistry. Experiments concluded that the formation of iron(II)-silicates were attributed to abiotic processes based on the Fe XAS spectra produced by the abiotic control experiments being similar in the shift in energy and spectral shape when compared to iron(II)-silicate standards and preserved nanoparticles from 2.5 Ga BIFs. The experimental conditions necessary for the substantial abiotic formation of iron(II)-silicates minerals associated with the formation of BIFs helped constrain ocean chemistry 2.5 Ga.

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