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

Language

English


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