HR: 0800h
AN: P51D-0950    [Abstracts]
TI: Modern Dolomitic Stromatolites from Lagoa Vermelha, Brazil
AU: * Vasconcelos, C
EM: cris.vasconcelos@erdw.ethz.ch
AF: Geological Institute, ETH-Zentrum, Zurich, 8092 Switzerland
AU: Visscher, P
EM: pieter.visscher@uconn.edu
AF: Department of Marine Sciences, University of Connecticut, Groton, 06340 United States
AU: Warthmann, R
EM: warthmann@erdw.ethz.ch
AF: Geological Institute, ETH-Zentrum, Zurich, 8092 Switzerland
AU: McKenzie, J A
EM: sediment@erdw.ethz.ch
AF: Geological Institute, ETH-Zentrum, Zurich, 8092 Switzerland
AB: Classic examples of modern stromatolites, such as those found in Shark Bay (Western, Australia) and Highborne Cay (Bahamas), furnish important insights to better interpret the environmental conditions of ancient biogeochemical process leading to calcification. Although these living examples may serve as modern analogues for ancient stromatolites, they do not precipitate primary dolomite, a carbonate mineral commonly found in Precambrian stromatolites and, thus, do not represent the full range of environmental conditions existing in early Earth history. Here, we report on the first recognized occurrence of microbiolite stromatolitic structures, associated with Ca-dolomite, growing in a hypersaline coastal lagoon, Lagoa Vermelha, near Rio de Janerio, Brazil. We examined the microbial community using microelectrode measurements, which indicate high rates of photosynthesis, aerobic respiration, sulfate reduction, sulfide oxidation and fermentation. The ratio between precipitation and dissolution inside the microbial mat has been estimated. The high pH recorded during daytime in the microbial mats reflects increased alkalinity associated with progressive increase of Mg in the mineral phase with depth below the surface, whereas the detection of zero-valent sulfur and polythionates produced by sulfide oxidizing bacteria indicates an additional process increasing alkalinity. Ca+2 microsensors studies and silver foil experiments, combined with the EDS/SEM examination of the biofilm, provide evidence also for the importance of EPS in the calcification processes. This geomicrobiology approach, linking studies of population, processes and products, permits us to estimate the role that specific microorganisms play during high Mg-calcite and Ca-dolomite precipitation. As dolomitic stromatolites were abundant in the Precambrian, the Lagoa Vermelha microbial community, which is adapted for survival under extreme salinity variations, may represent a modern analogue for a microcosm, which was active on the early Earth and may have evolved similarly in response to comparable extraterrestrial environments.
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