Date of Award:

5-2022

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Committee Chair(s)

Dennis Newell

Committee

Dennis Newell

Committee

Alexis Ault

Committee

Carol Dehler

Abstract

Isotopes are naturally occurring atoms of an element that vary in the number of neutrons present in their nuclei, resulting in different atomic masses. The most common stable isotopes of oxygen are oxygen-18 (18O) and oxygen-16 (16O). Geochemical processes, such as the formation of a solid mineral from dissolved elements in a fluid, can result in preferential concentration of one isotope over the other in a process known as fractionation. By measuring the ratio of 18O and 16O in solid minerals and using known fractionation values, the isotopic ratio of the fluid from which those minerals formed can be determined. Calculated values can then be compared to known isotopic ranges for different fluids (e.g., surface vs groundwaters).

In this study, we use the measured oxygen isotope ratios of iron oxide minerals (i.e., hematite) in rocks from the Boiler Room near Moab, Utah to determine the fluid(s) from which they formed and compare various proposed formation models. Ratios of stable isotopes for oxygen and iron, measurement of elemental concentrations, and textural observations of the rocks suggest that iron oxide minerals in the Boiler Room formed from a three-step process. First, a rock unit composed of carbonate minerals was deposited in a surface pond during the Jurassic period. After this unit was buried, an upward flowing acidic fluid dissolved the carbonate minerals within this layer. Changing geochemical conditions during this process caused iron dissolved in the acidic fluid to precipitate as hematite. Dissolution and replacement of the initially formed carbonate minerals resulted in the unique iron oxide rocks observed in the Boiler Room location where feeder pipes terminate into a horizontal layer of concentrated iron oxide. Understanding the formation processes of iron oxide minerals is important for reconstructing the history of fluid flow and mineral alteration in diverse geologic environments.

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