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Ediacaran iron formations and carbonates from Uruguay: palaeoceanographic, palaeoclimatic and palaeobiologic implications Open Access


Other title
Iron formations
Type of item
Degree grantor
University of Alberta
Author or creator
Pecoits, Ernesto
Supervisor and department
Konhauser, Kurt (Earth and Atmospheric Sciences)
Gingras, Murray (Earth and Atmospheric Sciences)
Examining committee member and department
Owttrim, George (Biological Sciences)
Konhauser, Kurt O. (Earth and Atmospheric Sciences)
Rosiere, Carlos A. (Universidade Federal of Minas Gerais)
Creaser, Robert (Earth and Atmospheric Sciences)
Gingras, Murray K. (Earth and Atmospheric Sciences)
Pemberton, George (Earth and Atmospheric Sciences)
Department of Earth and Atmospheric Sciences

Date accepted
Graduation date
Doctor of Philosophy
Degree level
The Ediacaran in Uruguay preserves a unique record of deposits generated during the assembly of the palaeocontinent Gondwana and concurrent with major changes in the atmosphere and oceans, and the rise of animal life. Recent studies have suggested that the deep oceans remained anoxic and highly ferruginous throughout the Ediacaran and possibly into the Cambrian. Unfortunately, acceptance of this idea has been hindered by the virtual absence of iron formations (IF). Detailed studies of Ediacaran IF in Uruguay confirm that ferruginous conditions dominated the pre-Gaskiers (~580 Ma), and interestingly, they also extended well into the upper Ediacaran before complete ocean ventilation occurred. Significantly, a simple twolayer stratified system that argues for an oxygenated surface layer overlying a suboxic zone is proposed. The association of negative δ13C excursions in Neoproterozoic carbonates and large-scale glaciations has become a tempting explanation for the short-term perturbation of the global carbon cycle. Not surprisingly, negative δ13C shifts in Ediacaran-aged carbonates from Uruguay have been interpreted as recording post-Gaskiers glacial events. New highresolution δ13C-chemostratigraphy of carbonates shows negative fractionations in deep facies with a progressive rise towards shallow-water settings, and suggests a deposition across a stratified ocean. Furthermore, 87Sr/86Sr chemostratigraphy coupled with radiometric data allowed a more precise chronostratigraphy, which supports an age of ~600-575 Ma for the unit, and suggests a deposition concurrent with the Gaskiers glaciation. Notwithstanding whether associated δ13C variations in shallow water facies were produced by glacially-related conditions or by the dynamic of the basin itself remains unresolved. Although these conclusions are particularly valid for these deposits, they carry important implications for the understanding of other negative δ13C excursions recorded in the Precambrian. Finally, bilaterian burrows occur in Gaskiers age glaciomarine rocks in Uruguay implying that these are the oldest definite animal tracks yet reported. Crucially, our new discovery unites the palaeontological and molecular data pertaining to the origin of bilaterians, and brings the origin of animals firmly into the interval of the Neoproterozoic glaciations. It also implies that ancestral bilaterians likely evolved first in relatively shallow seas, and only colonized the deep-sea floor once sufficient bottom water oxygenation had taken place.
License granted by Ernesto Pecoits ( on 2010-08-18T19:16:17Z (GMT): Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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