2006 Philadelphia Annual Meeting (2225 October 2006)
Paper No. 46-5
Presentation Time: 2:35 PM-2:50 PM

MULTI-STAGE EDIACARAN OCEAN OXIDATION AND ITS IMPACT ON EVOLUTIONARY RADIATION

FIKE, David, Earth, Atmospheric, & Planetary Sciences, MIT, 77 Massachusetts Ave., 54-812, Cambridge, MA 02139, dfike@mit.edu, GROTZINGER, John, Geological and Planetary Science, California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, PRATT, Lisa, IPTAI, Dept. of Geological Sciences, Indiana University, Bloomington, IN 47405, and SUMMONS, Roger, Earth and Planetary Sciences, Massachusetts Institute of Technology, 44 Carleton St, E34-246, Cambridge, MA 02138

Using high-resolution paired carbon (δ13Ccarb and δ13Corg) and sulfur (δ34SSO4 and δ34Spyr) isotopes, we can resolve a multi-stage record of Ediacaran ocean oxidation preserved in the strata of the Huqf Supergroup, Sultanate of Oman. Following the Marinoan glaciation, stage I oxidation lasts from ~ 635 610 million years ago (Myr) and records an increase in marine sulfate concentrations above ~ 200 μM, likely due to a rise in atmospheric oxygen. Stage II oxidation (~ 575 550 Myr) coincides with the Shuram excursion, a > 13 negative excursion in δ13Ccarb created by the oxidation of a large reservoir of deep ocean dissolved organic carbon (DOC). Support for more oxidizing conditions comes from a decrease in the fraction of sulfur buried as pyrite (fpyr) as well as a decrease in the abundance of both pyrite and TOC. The onset of stage II oxidation coincides with the evolution of acanthomorph acritarchs in Australia and China, and the appearance of the first Ediacaran metazoa, Charnia-type segmented fronds, while the first motile macroscopic metazoa (e.g., Kimberella) appear at ~555 Myr as the Shuram excursion draws to a close. Stage III oxidation (~ 550 547 Myr) is marked by presence of sulfur disproportionating metabolisms and the onset of co-variation in δ13Ccarb and δ13Corg, which are absent in older strata. Coincident with the onset of stage III oxidation, we see the evolution of macroscopic multicellular algae, an increase in the diversity of the acanthomorph acritarchs, and the appearance of the weakly calcifying metazoa Cloudina and Namacalathus. Following stage III oxidation, there is a period of quiescence characterized by little perturbation in the carbon cycle and an absence of significant evolutionary events. At ~542 Myr, anoxia at the Ediacaran-Cambrian boundary causes the extinction of the Ediacaran fauna, setting the stage for the Cambrian radiation.

2006 Philadelphia Annual Meeting (2225 October 2006)
General Information for this Meeting
Session No. 46
Changes in Ocean and Atmospheric Redox State and the Evolution of Life II
Pennsylvania Convention Center: 105 AB
1:30 PM-5:30 PM, Sunday, 22 October 2006

Geological Society of America Abstracts with Programs, Vol. 38, No. 7, p. 124

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