This research is focused on strata deposited in northern Utah during the Cryogenian Period (850 – 635 Ma) of the Neoproterozoic Era, a period that derives its name from the widespread evidence for multiple, likely global, glacial events during this time, commonly referred to as “Snowball Earth” glaciations. This dissertation includes detailed studies of two Cryogenian successions in northern Utah that bracket potential “Snowball Earth” events: the upper part of the Uinta Mountain Group (deposited prior to the glaciations) and the dolomite member of the Kelly Canyon formation (hypothesized to have formed in the aftermath of a global glaciation that terminated at either 665 or 635 Ma). Both successions contain a lithostratigraphic, geochemical, and biotic record of the Earth’s oceans before and after the largest-magnitude glaciations in the history of our planet.
The pre-glacial upper part of the Uinta Mountain Group in the area mapped for this study contains evidence of several (at least three) relatively short periods of ocean anoxia in which ferruginous conditions dominated and euxinia did not occur. There is no evidence that biota (organic-walled microfossil assemblages) were influenced by these brief anoxic events, but evidence from the composite Uinta Mountain Group stratigraphic record does suggest a gradual change in biota similar to that in the Chuar group. It is likely this biotic transition is related to nearshore eutrophication in the oceans, but additional redox geochemical information is needed to fully support this conclusion.
The dolomite member of the Kelley Canyon Formation on Antelope Island (post-glacial component of this study) contains idiosyncratic lithologic features thought to be characteristic of 635 Ma deglacial strata, yet its C-isotope values do not lend unequivocal support to this global correlation, and regional correlations and U-Pb zircon ages suggest it is ~30 million years older. These results challenge the popular notion that Neoproterozoic post-glacial cap carbonates can be correlated based upon their lithologic “style,” and they also lend additional support to the possibility of a “Snowball Earth” event at ~665 Ma.
| Identifer | oai:union.ndltd.org:UTAHS/oai:digitalcommons.usu.edu:etd-2699 |
| Date | 01 August 2013 |
| Creators | Hayes, Dawn Schmidli |
| Publisher | DigitalCommons@USU |
| Source Sets | Utah State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | All Graduate Theses and Dissertations |
| Rights | Copyright for this work is held by the author. Transmission or reproduction of materials protected by copyright beyond that allowed by fair use requires the written permission of the copyright owners. Works not in the public domain cannot be commercially exploited without permission of the copyright owner. Responsibility for any use rests exclusively with the user. For more information contact Andrew Wesolek (andrew.wesolek@usu.edu). |
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