Invited by Prof. El Albani, the Profesor Andrey BEKKER, from University of Manitoba, had a talk this morning 20th of february about Oxygen Overshoot and recovery in the Paleoproterozoic (2.5 – 2.0 billion years ago).
The conference is in english, introduction in french by Prof. El Albani.
Recorded the 20th of february 2013.
Videos of the conference bellow…
Séminary of Prof. Andrey BEKKER wednesday 20th of february 2013
Oxygen Overshoot and Recovery during the Early Paleoproterozoic.
During the Lomagundi Event, >2.22 to 2.06 Ga, marine carbonates recorded the largest and longest positive carbon isotope excursion, the earliest extensive marine sulfate evaporates were deposited, and the average Fe2O3/FeO ratio of shales increased dramatically. At the end of the Lomagundi Event, the first significant sedimentary phosphorites were deposited, and the carbon isotope values of marine carbonates returned to ~0‰ VPDB. Thereafter marine sulfate evaporates and phosphorites again became scarce, while the average Fe2O3/FeO ratio of shales decreased to intermediate values between those of the Archean and Lomagundi-age shales. We propose that the large isotopic and chemical excursions during the Lomagundi Event were caused by a positive feedback between the rise of atmospheric O2 level, the weathering of sulfides in pre-2.3 Ga sedimentary rocks, and the flux of phosphate to the oceans. The rise in the terrestrial phosphate flux led to an increase in the burial rate of organic carbon and a major transfer of oxygen from the carbon to the sulfur cycle.
The end of the Lomagundi Event was probably caused by a decrease in the terrestrial phosphate flux related to the weathering of low-pyrite sediments that were deposited during the Lomagundi Event. The rate of deposition of organic matter and burial rate of sulfate evaporates decreased, the isotopic and chemical excesses of the Lomagundi Event were eliminated, and the ocean-atmosphere system entered the period frequently called the Boring Billion.
Research interest of Pr Andrey BEKKER
Paleoproterozoic chemostratigraphy and event stratigraphy, climate changes in the deep past, rise in atmospheric oxygen, chemical composition of the atmosphere and ocean and its link with global tectonics, ocean redox state in the Precambrian, C, S, and Fe cycles, first appearance of marine sulfate evaporites, sedimentary mineral deposits, stable isotope geochemistry.
Javaux, E.J., Marschall, C.P., Bekker, A., 2010, Organic-walled microfossils in 3.2-billion-year-old shallow-marine siliciclastic deposis, Nature, v. 463, p. 934-938. Javaux et al., 2010.pdf
Bekker, A., Barley, M.E., Fiorentini, M.L., Rouxel, O.J., Rumble, D., and Beresford, S.W., 2009, Atmospheric Sulfur in Archean Komatiite-Hosted Nickel Deposits, Science, in the press.Bekker et al., 2009.pdf
Hofmann, A., Bekker, A., Rouxel, O., Rumble, D., Master, S., 2009, Multiple sulphur and iron isotope composition of detrital pyrite in Archaean sedimentary rocks: A new tool for provenance analysis, EPSL, v. 286, p. 436-445. Hofmann et al., 2009.pdf
Planavsky, N., Rouxel, O., Bekker, A., Shapiro, R., Fralick, P., Knudsen, A., 2009, Iron-oxidizing microbial ecosystems trived in late Paleoproterozoic redox-stratified oceans, EPSL, v. 286, p. 230-242.Planavsky et al., 2009.pdf
Yang, G., Hannah, J.L., Zimmerman, A., Stein, H.J., Bekker, A., 2009, Re-Os depositional age for Archean carbonaceous slates from the southwestern Superior Province: Challenges and insights, EPSL, v. 280, p. 83-92.Yang et al., 2009.pdf
Slack, J.F., Grenne, T., Bekker, A., 2009, Seafloor-hydrothermal Si-Fe-Mn exhalites in the Pecos greenstone belt, New Mexico, and the redox state of ca. 1720 Ma deep seawater, Geosphere, v. 5(3), p. 302-314.Slack et al., 2009.pdf
Pollack, G.D., Krogstad, E.J., Bekker, A., 2009, U-Th-Pb-REE systematics of organic-rich shales from the ca. 2.15 Ga Sengoma Argillite Formation, Botswana: Evidence for oxidative continental weathering during the Great Oxidation Event, Chemical Geology, v. 260, p. 172-185.Pollack et al., 2009.pdf
Guo, Q., Strauss, H., Kaufman, A.J., Schröder, S., Gutzmer, J., Wing, B., Baker, M.A., Bekker, A., Kim, S.-T., Farquhar, J., 2009, Reconstructing Earth’s surface oxidation across the Archean-Proterozoic transition, Geology, v. 37 (5), p. 399-402.Guo et al., 2009.pdf
Bekker, A., Holmden, C., Beukes, N.J., Kenig, F., Eglington, B., Patterson, W.P., 2008, Fractionation between inorganic and organic carbon during the Lomagundi (2.22-2.1 Ga) carbon isotope excursion, EPSL, v. 271, p. 278-291.Bekker et al., 2008.pdf
Scott, C., Lyons, T.W., Bekker, A., Shen, Y., Poulton, S., Chu, X., and Anbar, A., 2008, Tracing the stepwise oxygenation of the Proterozoic biosphere, Nature, v. 452, p. 456-459.Scott et al., 2008.pdf