HR: 14:40h
AN: B23G-05    [Abstracts]
TI: Widespread Iron Oxidizing Bacterial Communities in a late Paleoproterozoic Marine Environment
AU: * Planavsky, N
EM: planavsky@gmail.com
AF: University of California, Riverside, 900 University Avenue, Riverside, CA 92521, United States
AU: Rouxel, O
EM: orouxel@whoi.edu
AF: Woods Hole Oceanographic Institution, 266 Woods Hole Road, Woods Hole, MA 02543, United States
AU: Bekker, A
EM: abekker@ciw.edu
AF: University of Manitoba, Department of Geological, Winnipeg, MB R3T 2N2, Canada
AB: Discovery of exceptionally well-preserved microfossils in the Gunflint Iron Formation provided the first evidence for diverse and abundant life in the Precambrian oceans. However, whether the Gunflint microbial communities were dominated by cyanobacteria or represent an archaic, lithotrophic ecosystem is a matter of longstanding debate. Here, we present Fe isotope and rare earth element (REE) data for microfossiliferous stromatolites that are consistent with the Gunflint biota being an iron-oxidizing bacterial community. The lack of or positive Ce anomalies in REE data indicate that the benthic community grew below a redoxcline and positive iron isotope compositions reveal that the microbial community only oxidized a fraction of the dissolved iron load. This depositional setting and Fe isotope evidence for incomplete iron oxidation are inconsistent with a cyanobacterial interpretation and provide strong support that the Gunflint biota was indeed a microaerophilic lithotrophic microbial ecosystem. An apparently restricted temporal distribution of the Gunflint biota coupled with a widespread spatial distribution signals a significant ecosystem evolutionary event in the late Paleoproterozoic when the ocean was redox-stratified and Fe-rich anoxic waters impinged onto the shallow shelf.
DE: 0404 Anoxic and hypoxic environments (4802, 4834)
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0424 Biosignatures and proxies
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting