Aquatic Sciences Meeting, Albuquerque 2001

SS43 Biogeochemical Processes in Stromatolites: A 3 b.y.old ecosystem (Spatial and Temporal Connections)

Date: Monday, February 12, 2001, Time: 2:00:00 PM

Location: Cimarron

Reid, R, P, University of Miaim, Miami, USA, preid@rsmas.miami.edu

MICROBIAL - ENVIRONMENTAL INTERACTIONS FORMING STROMATOLITES IN MODERN MARINE ENVIRONMENTS

Interpretation of ancient stromatolites is hampered by limited knowledge of the relative roles played by microbial and environmental processes in their formation. Recent results from the Research Initiative on Bahamian Stromatolites (RIBS) project show that formation of modern marine stromatolites in Exuma Cays results from cycling between three microbial mat communities: (1) a ‘pioneer community’ of filamentous cyanobacteria, which traps and binds sediment grains; (2) a microbial ‘biofilm community’ that develops during hiatuses in sediment accretion and which forms thin micritic crusts; and (3) a ‘climax community’, which includes abundant endolithic coccoid cyanobacteria and which forms lithified layers of fused grains during prolonged hiatal periods. Preservation of lithifed layers at depth creates a laminated microfabric. Based on these findings, we argue that growth of laminated microbial structures with topographic relief, such as those that dominated the fossil record for three billion years, depends on early lithification of surface mats. We propose that this lithification process occurs, at least in part, by decomposition of an amorphous matrix of bacterial exopolymer (not sheath material) in the photic zone across the stromatolite surface.

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Aquatic Sciences Meeting, Albuquerque 2001

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