Award Date
December 2015
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Geoscience
First Committee Member
Ganqing Jiang
Second Committee Member
Ganqing Jiang
Third Committee Member
Steven Rowland
Fourth Committee Member
Michael Wells
Fifth Committee Member
Tomothy Lyons
Sixth Committee Member
Brian Hedlund
Number of Pages
204
Abstract
The relative role that environmental versus intrinsic biological factors played in
shaping the history of life on Earth is a fundamental but unanswered question in the
natural sciences. Most famously, it has been heavily debated if the emergence and
diversification of early animals during the Ediacaran Period (ca. 635–541 Ma) was tied to
a rise in atmospheric-oceanic oxygen levels. Temporally discontinuous geochemical data and patchy fossil record in literature are inadequate to chart the Ediacaran redox history and its causal relationship with the biotic evolution. My PhD study aims for a multiproxy geochemical record within a well-established stratigraphic framework of the
Ediacaran (ca. 635–541 Ma) succession in South China. This succession is particularly
suited for obtaining a high-resolution redox record based on redox-sensitive trace
elements (RSEs) and pyrite sulfur isotopes due to the availability of organic-rich black
shales. Modern-level RSE enrichments in black shales immediately overlying the
Marinoan-age glacial diamictites reveal, for the first time, a pervasive ocean oxygenation
event in the aftermath of the Earth’s extreme cold. This oxygenation event may have
triggered the first appearance of primitive animals in Earth history. Following this
oxygenation, RSE concentrations returned back to crustal and near-crustal values until the middle Ediacaran (ca. 580 Ma), implying significant ocean anoxia. Low RSE values
appear again after spikes at ca. 580 Ma and ca. 550 Ma. The rises and falls of RSEs and
pyrite sulfur isotopes document a dynamic Ediacaran (and likely including Cambrian)
ocean redox state: multiple oxygenation events in the overall anoxic Ediacaran ocean.
The brief (<5–10 Ma) oxygenation events may have triggered staged biotic innovations
separated by long-term evolutionary stasis.
Keywords
Anoxia; Biogeochemistry; Doushantuo; Ediacaran; Redox
Disciplines
Geochemistry | Geology | Sedimentology
File Format
Degree Grantor
University of Nevada, Las Vegas
Language
English
Repository Citation
Sahoo, Swapan Kumar, "Ediacaran ocean redox evolution" (2015). UNLV Theses, Dissertations, Professional Papers, and Capstones. 2577.
http://dx.doi.org/10.34917/8220158
Rights
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