Publication Date
5-2025
Date of Final Oral Examination (Defense)
3-5-2025
Type of Culminating Activity
Dissertation
Degree Title
Doctor of Philosophy in Geosciences
Department
Geosciences
Supervisory Committee Chair
Mark D. Schmitz, Ph.D.
Supervisory Committee Member
James L. Crowley, Ph.D.
Supervisory Committee Member
Clyde J. Northup, Ph.D.
Supervisory Committee Member
V. Dorsey Wanless, Ph.D.
Abstract
The rock record is the archive of events and processes that control the evolution of our ever-changing planet; from granites born deep in the heart of an orogenic belt under tremendous heat and pressure to sandstones deposited on a quiescent passive margin. A long-held question in geology is how do we transpose this rock record into time? It is not a simple question as the Earth operates on many different timescales, from the timescale of burial during orogenesis, to the timescale of deposition during sea level rise, to the timescale of biotic evolution. There are indicators all around us that provide a relative timescale when viewed through the laws of superposition, cross-cutting relationships, and inclusion. However, these do not provide a numerical timescale; for that we must harness the spontaneous decay of unstable radionuclides. The steady radioactive decay of uranium to lead within the zircon lattice as long been known as a chronometer able to record numerical time on the scale of millions to billions of years. The gold standard method for making these measurements is chemical abrasion isotope dilution thermal ionization mass spectrometry, which can be complemented with microbeam methods like laser ablation inductively coupled plasma mass spectrometry place to numerical constraints on the timing and duration of Earth processes in deep time. The chapters below describe my use of U-Pb geochronology using both techniques to explore the timescales of diverse earth processes.
In chapter one of my dissertation, I outline the methods, results, and implications of high-precision U-Pb geochronology and Bayesian age modeling applied to different temporal-scales and geologic processes preserved in rocks of the American west. In chapter two, I develop a novel application of high-precision U-Pb zircon geochronology, high resolution trilobite biostratigraphic compilations, and Bayesian age modeling to refine the global Furongian (late Cambrian) timescale, and the timing, duration, and causes of the Steptoean Positive Isotopic Carbon Excursion (SPICE) from a stratigraphic section in northeastern Utah. In chapter three I take the methods explored in chapter two and apply them to the unique stratigraphic record of the Cambrian Tonto Group of Grand Canyon. In doing so, I created the first lateral Bayesian age model, which has implications for the tempo of the Sauk transgressions, the Cambrian Explosion, associated global carbon cycle perturbations, and the Miaolingian timescale. In chapter four I present high-precision U-Pb zircon and titanite geochronology from Proterozoic rocks of the Lower Granite Gorge of the Grand Canyon, which archive the assembly of the North American continent. The new radioisotopic ages presented herein offer a unique snapshot into the timescales of middle crustal tectonometamorphic processes during orogenesis.
DOI
10.18122/td.2368.boisestate
Recommended Citation
Farrell, Thomas Patrick, "Numerical Calibration of the Cambrian Earth-System and Paleoproterozoic Assembly of Western Laurentia via High-Precision U-Pb Geochronology" (2025). Boise State University Theses and Dissertations. 2368.
10.18122/td.2368.boisestate
Comments
https://orcid.org/0000-0002-6277-4533