Paper No. 280-10
Presentation Time: 10:30 AM
TRACING EARTH’S O2 EVOLUTION USING ZN/FE SYSTEMATICS IN MARINE CARBONATES
LIU, Xiao-Ming, Department of Geological Sciences, University of North Carolina, Chapel Hill, Chapel Hill, NC 27599-3315, KAH, Linda C., Earth and Planetary Sciences, University of Tennessee, 1412 Circle Drive, Knoxville, TN 37996, KNOLL, Andrew H., Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, CUI, Huan, Department of Geology, University of Maryland, College Park, MD 20742, KAUFMAN, Alan J., Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD 20742, SHAHAR, Anat, Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015 and HAZEN, Robert M., Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington DC, 20015, xiaomliu@unc.edu
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 O
2, 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.
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