Application of the Rhenium-Osmium Isotope Geochronometer to Neoproterozoic and Paleozoic Organic Rich Mudrocks



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New Re-Os isotope data on organic-rich mudrocks (ORMs) from the Neoproterozoic Upper Fifteenmile Group, Coal Creek Inlier, Yukon Territory, Canada and the Paleozoic Quamby Fm., Turnbridge Borehole, Tasmania yield depositional model ages, which help to deconvolve the timing of complex tectonic and climatic changes in earth history. The Neoproterozoic Upper Fifteenmile Group has Re-Os depositional model age of 764 ±51 Ma (2σ; Model-1; MSWD 4.2; Osi 0.37 ±0.19). The age obtained is identical to ages from the same horizon across northwestern Canada. This result provides direct age control for biomineralizing microfossils and the Bitter Springs isotopic stage. If these model ages are correct, the Bitter Springs isotopic stage may be related to the Kiagas age glacial events in Africa and South America. The Paleozoic Quamby Fm. has a Re-Os model age of 294 ±29Ma (2σ; Model-3; MSWD 4.2; Osi 0.58 ±0.14). This result is the first radiometric age obtained for the Quamby Fm. and is in good agreement with biostratigraphic control that suggests an Asselian age. This result also suggests that the end of the Late Paleozoic Ice Age in Tasmania is synchronous with other glacial deposits across Australia. In addition to discussing the implications of these Re-Os results, this thesis discusses the development of the Re-Os analytical method at the University of Houston.



Geochronology, Cryogenian, Rhenium, Osmium, Snowball earth, Bitter springs stage, Organic rich mudrock