Date of Award:
Master of Science (MS)
W. David Liddell
W. David Liddell
Carol M. Dehler
Robert Q. Oaks Jr.
The Ordovician Garden City Formation is a mostly marine limestone rock formation deposited in what is known today as the Northern Utah Basin in North America ~485.5 million years ago. Previous research on the Pogonip Group, a time equivalent rock formation located in the Ibex Basin south of the Northern Utah Basin, has identified nine cycles of sea-level fall and rise. However, these nine sea-level cycles have proven difficult to identify within the Garden City Formation due to the limited contrast between rock types within the rock formation. Previous research on the Garden City has approximated these sea-level cycles through rock chemistry and fossils by comparing known zones of fossils and negative and positive spikes in rock chemistry data with similar data from the Pogonip Group. However, traditional methods of identifying sea-level cyclicity by looking for changes in the limestone rocks are not easily applied to the Garden City Formation because highly turbulent internal ocean waves have reworked the original deposits of the formation. This study examines the lithology and geochemistry to determine previously unrecognized sea-level cycles and compare previous depositional models.
A positive spike in carbon stable-isotope data found near the base of the Garden City Formation is traceable to the Pogonip Group and other rock formations in Argentina and China. This same positive carbon stable-isotope spike may also provide evidence for a global cooling event.
Three instances of sea-level fall were identified in the Garden City Formation. However, these sea-level falls were only identifiable through carbon stable-isotope data and major changes of rock type. A sea-level curve for the Garden City Formation based on rock type does show an overall fall in sea level and resembles the Pogonip Group and global curves.
Kehoe, Kenneth W., "Lithological and Geochemical Characterization of Ramp Sediments and a Depositional Model of the Ordovicain Garden City Formation, Northeastern Utah" (2021). All Graduate Theses and Dissertations. 8357.
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