HR: 0800h
AN: P51D-0952    [Abstracts]
TI: Microbial Mediated Mineralization in the Extreme Hypersaline Sabkha Environment of Abu Dhabi (UAE)
AU: * Bontognali, T
EM: tomaso.bontognali@erdw.ethz.ch
AF: Geological Institute, ETH-Zentrum, Zurich, 8092 Switzerland
AU: McKenzie, J
EM: sediment@erdw.ethz.ch
AF: Geological Institute, ETH-Zentrum, Zurich, 8092 Switzerland
AU: Warthmann, R
EM: warthmann@erdw.ethz.ch
AF: Geological Institute, ETH-Zentrum, Zurich, 8092 Switzerland
AU: Vasconcelos, C
EM: cris.vasconcelos@erdw.ethz.ch
AF: Geological Institute, ETH-Zentrum, Zurich, 8092 Switzerland
AB: Studies of microbes living in extreme environments provide important information about microbial metabolisms, survival strategies and production of biominerals. Knowledge of these geobiological processes and the ultimate product can be used to better reconstruct the evolution of life during the early Earth, when skeletal fossils are absent. Our study focuses on a well-documented extreme hypersaline environment, the coastal sabkhas of Abu Dhabi (UAE), which is among the rare geological settings where primary dolomite is forming today. The origin of dolomite still remains one of the most debated subjects in sedimentary geology. Although microbial mediation is proposed as a solution for this controversy, the relationship between microbial activity and dolomite precipitation in the sabkha environment has not been fully evaluated. The goal of this study is to investigate this microbial dolomite factor combining sedimentological, geochemical and microbiological approaches. Preliminary results indicate the existence of a new dolomite facies consisting of dolomite spheres enveloped in a biofilm. This association is evidence supporting the microbial hypothesis of dolomite formation. Together with other evaporite minerals, the spheres grow in situ accumulating between 10 and 40 cm depth below the sabkha surface in an organic carbon-rich sediment. The co-existence of dolomite with gypsum leads us to hypothesize a link between the C and S cycles under hypersaline conditions. We propose that formation of significant amounts of gypsum within the zone of dolomite precipitation could be related to the recycling of S compounds during microbial metabolism, such as a combination of sulfate reduction and sulfide oxidation, which could lead to the retention of S in the system. Additionally, the EPS included within the biofilm is widely recognized as an important organic component involved in the precipitation of carbonates. EDS/SEM studies of the biofilm encompassing the dolomite indicate that Mg ions with respect to Ca ions are preferentially bound to the EPS structure, which could provide an ideal template for dolomite precipitation, and further confirms the hypothesis that EPS plays a key role in microbial mediated carbonate precipitation. Using a microbial approach to reinvestigate dolomite formation beneath the sabkha surface will undoubtedly expand our understanding of the biogeochemical changes occurring in such extreme hypersaline environments and may even provide new interpretations of evaporite mineral associations commonly found in the terrestrial rock record. Indeed, similar evaporite mineral associations may be even more common in extraterrestrial environments, as evidenced by recent observations of evaporitic sediments on Mars.
DE: 0419 Biomineralization
DE: 0448 Geomicrobiology
DE: 0456 Life in extreme environments
DE: 0463 Microbe/mineral interactions
SC: Planetary Sciences [P]
MN: Fall Meeting 2005