Geological Society of America

T280 Geobiology of Critical Transitions: Integrating Fossils, Proxies, and Models II

Wednesday, 4 November 2015
8:00 AM - 12:00 PM
Room 325/326

TRACING EARTH’S O2 EVOLUTION USING ZN/FE SYSTEMATICS IN MARINE CARBONATES

Paper number: T280-11
Program: Technical Sessions
Time: 10:30 AM – 10:45 AM

Authors

Xiao-Ming Liu Presenting Author
University of North Carolina, Chapel Hill, Chapel Hill, NC
Linda C. Kah
University of Tennessee, Knoxville, TN
Andrew H. Knoll
Harvard University, Cambridge, MA
Huan Cui
University of Maryland, College Park, MD
Alan Kaufman
University of Maryland, College Park, MD
Anat Shahar
Carnegie Institution of Washington, Washington, DC
Robert M. Hazen
Carnegie Institution of Washington, Washington DC

Abstract

Redox sensitive major and trace elements in sedimentary records (e.g. BIFs, black shales) have been developed as proxies to reconstruct paleoenvironmental information in deep time [1, 2]. However, many of the sedimentary records are underepresented during some geological time perids. For example, during the “boring billion” (1.8 ~ 0.8 Ga), global high sea-level limits the presence of deep sea black shales. In contrast, carbonate rocks are pervasive through Earth’s history and can provide additional information on paleoenvironments, such as seawater chemistry and/or atmospheric O₂, during the evolution of Earth.

We analyzed the major and trace element concentrations in micro-drilled, well-characterized carbonate rocks from around the world throughout Mesozoic, Paleozoic and Precambrian. In particular, we explored the use of Zn/Fe ratios as redox proxies to trace redox-state of seawater evolution. We observed a two step increase of mean Zn/Fe ratios in carbonates through Earth’s history, which correponds with two major oxdiation events (the Great Oxidiation Event and Neoproterozic Oxidation Event, respectively). We have carefully screened these carboantes for possible late digenetic effects and hydrothermal alterations. In addition, it is very unlikely that change of depositional environments, secular evolution of mantle and continental inputs greatly influenced the observation trace element behavior. Therefore, Zn/Fe ratios in these shallow marine carbonates have the potential to be a useful tracer for atmosphereic O₂ evolution, which potentially provides a tool in quantatively evaluting secular evolution of Earth’s atmospheric O₂.

References:

[1] Sahoo et al. (2012) Ocean oxygenation in the wake of the Marinoan glaciation. Nature 489:546-549. [2] Konhauser et al. (2009) Oceanic nickel depletion and a methanogen famine before the Great Oxidation Event. Nature 458:750-753.