| Summary: | Cryogenian Snowball Earth glaciations are some of the most extreme changes in Earth’s climate through its history. Decades of work have established the global ubiquity of Snowball Earth sedimentary deposits and their synchroneity in time, yet key questions remain concerning the potential causes for global glaciations and their drastically different durations and expressions in the rock record. This dissertation addresses these questions and proposes explanations for the onset of global glaciation and how the abrupt termination of a Snowball event could explain the differences in chemical sediments seen between the two Cryogenian Snowball events. In Chapter 1, I evaluate the emplacement of a large igneous province as a potential trigger for the Sturtian Snowball Earth (717-661 Ma). This work was done in collaboration with Francis A. Macdonald, Mark D. Schmitz, Robert H. Rainbird, Wouter Bleeker, Barra A. Peak, Rebecca M. Flowers, Paul F. Hoffman, Matthew Rioux, and Michael A. Hamilton. Previous geochronology has suggested a rough coincidence of glacial onset with one of the largest magmatic episodes in the geological record, the Franklin large igneous province. I show that chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb geochronology on zircon and baddeleyite from sills associated with the paleo-equatorial Franklin large igneous province in Arctic Canada record rapid emplacement between 719.86 ± 0.21 and 718.61 ± 0.30 Ma ago, 0.9 to 1.6 Ma before the onset of widespread glaciation. Geologic observations and (U-Th)/He dates on Franklin sills are compatible with major post–Franklin exhumation, possibly due to development of mafic volcanic highlands on windward equatorial Laurentia and increased global weatherability. After a transient magmatic CO2 flux, long-term carbon sequestration associated with increased weatherability could have nudged Earth over the threshold for runaway ice-albedo feedback.In Chapter 2, I address whether there is evidence for glaciations in the 50 ...
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