Date of Award:

5-2021

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Committee Chair(s)

Carol M. Dehler

Committee

Carol M. Dehler

Committee

James P. Evans

Committee

Adolph W. Yonkee

Abstract

The Snowball Earth Hypothesis details a time in Earth’s history (the Cryogenian period) where the entire planet was encapsulated by kilometer thick ice sheets for two, multi-million-year glaciations. The first, known as the Sturtian, lasted from 717 – 660 million years ago while the second, known as the Marinoan, lasted form approximately 650 – 635 million years ago. Snowball Earth was caused by a few processes that sort of built upon each other: Rodinia began splitting apart ~740 million years ago which allowed for increased rates of silicate weathering. High rates of silicate weathering resulted in CO2 drawdown which in turn caused the global temperature to drop. The gradual drop in temperature allowed for polar ice to advance and, once the ice reached a critical latitude, the earth experienced a runaway ice albedo effect – meaning ice advanced uncontrollably all the way to the equator – resulting in a completely ice-covered planet.

Evidence for Snowball Earth comes in the form of paleomagnetic data that show that Rodinia was rifting at this time, a global distribution and synchroneity of Snowball Earth deposits, carbon isotope ratios, and cap carbonates (a unique lithology present only in Snowball Earth deposits). In Pocatello, Idaho, geologists have identified deposits (the Pocatello Formation) that fall within the age range of Snowball Earth and that exhibit similar lithologic characteristics to other known Snowball Earth deposits. The goal of this study is to determine whether the Pocatello Formation was deposited during Snowball Earth, and if it is, which glaciation(s)/deglaciation(s) it was deposited during. To accomplish this goal, we conducted field work to characterize the different lithologies of the Pocatello Formation and then we used a radiometric dating technique called chemical abrasion – isotope dilution – thermal ionization mass-spectrometry to find out exactly how old the Pocatello Formaton is.

Our results show that the Pocatello Formation is host to Sturtian glacial deposits, Marinoan glacial deposits, and Marinoan deglacial deposits. These findings will allow for: the revision to local stratigraphy and age boundaries, correlation of the Pocatello Formation with other Snowball Earth deposits worldwide, and further insight into the Cryogenian period.

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