2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 109-5
Presentation Time: 9:00 AM

δ13C OF TERRESTRIAL ORGANIC MATTER AS A PROXY FOR ATMOSPHERIC OXYGEN IN THE PHANEROZOIC


MUEHLENBACHS, Karlis1, TAPPERT, Ralf2, MCKELLAR, Ryan C.3, WOLFE, Alexander P.4, TAPPERT, Michelle C.4 and SCHOELL, Martin5, (1)Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 ESB, Edmonton, AB T6G 2E3, (2)Institute of Mineralogy & Petrography, Universität Innsbruck, Innsbruck, A-6020, Austria, (3)Royal Saskatchewan Museum, Regina, SK T6G 2E3, Canada, (4)Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada, (5)GeoConsult International Inc, Berkley, CA 94705

The carbon isotope composition (δ13C) of terrestrial organic carbon varied considerably throughout the Phanerozoic. These variations primarily reflect changes in 13C-fractionation during photosynthesis by C3 plants—the main contributors to terrestrial organic matter—and this is in part linked to changes in atmospheric composition. We reconstructed the partial pressure of atmospheric oxygen (pO2) since the emergence of land plants in the Ordovician following the approach of Tappert et al. [1], using the published δ13C record of fossil resins (amber), coals and dispersed terrestrial organic matter. For most of this time, atmospheric pO2 was considerably lower (pO2~10-21%) compared to today (pO2=21%). Secular variations in pO2 must reflect changing amounts of burial of organic matter and sulfides. We observe a strong correlation between pO2 calculated from land plants, and the strontium and lithium isotopic compositions of marine carbonates. The marine Sr and Li isotope record reflects continental weathering and diagenesis driven by tectonic activity and mountain building. Its synchronicity with pO2 implies that tectonics and mountain building control not only the volume of weathering and sedimentation, but also the proportion of the biomass that is buried on geological timescales.

[1] Tappert et al. (2013) Geochim. Cosmochim. Acta 121, 240-262.

Session No. 109

T212. Co-Evolution on Earth’s Surface: Terrestrial Ecosystem and Environmental Interactions I
Monday, 20 October 2014: 8:00 AM-12:00 PM
219 (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.280
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